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 $85.56   3.294%   $88.3783   $88.38   $88.40   $88.40  
  Purchase #2 $130.67   8.193%   $141.3758   $141.38   $141.40   $141.40  
  Purchase #3 $119.83   12.839%   $135.215   $135.22   $135.20   $135.20  
  Purchase #4 $151.95   7.260%   $162.9816   $162.98   $163.00   $163.00  
  Purchase #5 $181.35   7.432%   $194.8279   $194.83   $194.85   $194.80  
  Purchase #6 $199.65   3.562%   $206.7615   $206.76   $206.75   $206.80  
  Purchase #7 $107.85   7.213%   $115.6292   $115.63   $115.65   $115.60  
  7 purchase totals = $976.86       $1,045.1693   $1,045.18   $1,045.25   $1,045.20