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 $60.45   8.146%   $65.3743   $65.37   $65.35   $65.40  
  Purchase #2 $234.95   13.420%   $266.4803   $266.48   $266.50   $266.50  
  Purchase #3 $10.69   3.341%   $11.0472   $11.05   $11.05   $11.00  
  Purchase #4 $230.71   5.501%   $243.4014   $243.40   $243.40   $243.40  
  Purchase #5 $148.58   6.869%   $158.786   $158.79   $158.80   $158.80  
  Purchase #6 $11.87   7.725%   $12.787   $12.79   $12.80   $12.80  
  Purchase #7 $91.36   4.279%   $95.2693   $95.27   $95.25   $95.30  
  7 purchase totals = $788.61       $853.1455   $853.15   $853.15   $853.20