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 $55.48   6.250%   $58.9475   $58.95   $58.95   $58.90  
  Purchase #2 $172.46   7.240%   $184.9461   $184.95   $184.95   $184.90  
  Purchase #3 $117.28   7.652%   $126.2543   $126.25   $126.25   $126.30  
  Purchase #4 $101.89   8.386%   $110.4345   $110.43   $110.45   $110.40  
  Purchase #5 $114.65   6.525%   $122.1309   $122.13   $122.15   $122.10  
  Purchase #6 $238.49   10.279%   $263.0044   $263.00   $263.00   $263.00  
  Purchase #7 $13.69   10.747%   $15.1613   $15.16   $15.15   $15.20  
  7 purchase totals = $813.94       $880.8790   $880.87   $880.90   $880.80