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 $94.97   5.447%   $100.143   $100.14   $100.15   $100.10  
  Purchase #2 $124.47   3.724%   $129.1053   $129.11   $129.10   $129.10  
  Purchase #3 $150.66   11.171%   $167.4902   $167.49   $167.50   $167.50  
  Purchase #4 $94.36   9.774%   $103.5827   $103.58   $103.60   $103.60  
  Purchase #5 $56.75   10.124%   $62.4954   $62.50   $62.50   $62.50  
  Purchase #6 $44.26   4.297%   $46.1619   $46.16   $46.15   $46.20  
  Purchase #7 $229.51   10.675%   $254.0102   $254.01   $254.00   $254.00  
  7 purchase totals = $794.98       $862.9887   $862.99   $863.00   $863.00