Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $167.94   9.594%   $184.0522   $184.05   $184.05   $184.10  
  Purchase #2 $127.92   13.638%   $145.3657   $145.37   $145.35   $145.40  
  Purchase #3 $141.76   4.547%   $148.2058   $148.21   $148.20   $148.20  
  Purchase #4 $248.86   3.366%   $257.2366   $257.24   $257.25   $257.20  
  Purchase #5 $104.87   7.299%   $112.5245   $112.52   $112.50   $112.50  
  Purchase #6 $100.25   13.313%   $113.5963   $113.60   $113.60   $113.60  
  Purchase #7 $132.86   10.450%   $146.7439   $146.74   $146.75   $146.70  
  7 purchase totals = $1,024.46       $1,107.7250   $1,107.73   $1,107.70   $1,107.70