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 $101.32   6.209%   $107.611   $107.61   $107.60   $107.60  
  Purchase #2 $150.31   4.222%   $156.6561   $156.66   $156.65   $156.70  
  Purchase #3 $67.84   9.219%   $74.0942   $74.09   $74.10   $74.10  
  Purchase #4 $122.47   11.302%   $136.3116   $136.31   $136.30   $136.30  
  Purchase #5 $150.32   6.842%   $160.6049   $160.60   $160.60   $160.60  
  Purchase #6 $110.99   13.340%   $125.7961   $125.80   $125.80   $125.80  
  Purchase #7 $43.33   8.346%   $46.9463   $46.95   $46.95   $46.90  
  7 purchase totals = $746.58       $808.0202   $808.02   $808.00   $808.00