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 $190.68   6.163%   $202.4316   $202.43   $202.45   $202.40  
  Purchase #2 $80.89   6.279%   $85.9691   $85.97   $85.95   $86.00  
  Purchase #3 $106.43   10.250%   $117.3391   $117.34   $117.35   $117.30  
  Purchase #4 $55.26   7.291%   $59.289   $59.29   $59.30   $59.30  
  Purchase #5 $96.32   13.696%   $109.512   $109.51   $109.50   $109.50  
  Purchase #6 $112.78   10.806%   $124.967   $124.97   $124.95   $125.00  
  Purchase #7 $164.31   8.217%   $177.8114   $177.81   $177.80   $177.80  
  7 purchase totals = $806.67       $877.3192   $877.32   $877.30   $877.30