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 $220.58   7.451%   $237.0154   $237.02   $237.00   $237.00  
  Purchase #2 $34.76   4.607%   $36.3614   $36.36   $36.35   $36.40  
  Purchase #3 $233.51   5.481%   $246.3087   $246.31   $246.30   $246.30  
  Purchase #4 $24.71   7.586%   $26.5845   $26.58   $26.60   $26.60  
  Purchase #5 $89.70   6.460%   $95.4946   $95.49   $95.50   $95.50  
  Purchase #6 $173.56   8.273%   $187.9186   $187.92   $187.90   $187.90  
  Purchase #7 $243.57   13.115%   $275.5142   $275.51   $275.50   $275.50  
  7 purchase totals = $1,020.39       $1,105.1974   $1,105.19   $1,105.15   $1,105.20