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 $57.58   11.349%   $64.1148   $64.11   $64.10   $64.10  
  Purchase #2 $117.26   7.451%   $125.997   $126.00   $126.00   $126.00  
  Purchase #3 $53.37   13.761%   $60.7142   $60.71   $60.70   $60.70  
  Purchase #4 $85.85   13.582%   $97.5101   $97.51   $97.50   $97.50  
  Purchase #5 $183.88   13.831%   $209.3124   $209.31   $209.30   $209.30  
  Purchase #6 $214.26   5.507%   $226.0593   $226.06   $226.05   $226.10  
  Purchase #7 $116.77   3.188%   $120.4926   $120.49   $120.50   $120.50  
  7 purchase totals = $828.97       $904.2004   $904.19   $904.15   $904.20