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 $87.45   9.766%   $95.9904   $95.99   $96.00   $96.00  
  Purchase #2 $110.32   12.734%   $124.3681   $124.37   $124.35   $124.40  
  Purchase #3 $181.81   13.261%   $205.9198   $205.92   $205.90   $205.90  
  Purchase #4 $37.31   10.296%   $41.1514   $41.15   $41.15   $41.20  
  Purchase #5 $44.40   9.615%   $48.6691   $48.67   $48.65   $48.70  
  Purchase #6 $41.36   12.462%   $46.5143   $46.51   $46.50   $46.50  
  Purchase #7 $117.80   4.140%   $122.6769   $122.68   $122.70   $122.70  
  7 purchase totals = $620.45       $685.2900   $685.29   $685.25   $685.40