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 $59.93   6.826%   $64.0208   $64.02   $64.00   $64.00  
  Purchase #2 $182.80   9.460%   $200.0929   $200.09   $200.10   $200.10  
  Purchase #3 $80.45   8.708%   $87.4556   $87.46   $87.45   $87.50  
  Purchase #4 $168.30   12.247%   $188.9117   $188.91   $188.90   $188.90  
  Purchase #5 $114.35   6.244%   $121.49   $121.49   $121.50   $121.50  
  Purchase #6 $109.65   13.283%   $124.2148   $124.21   $124.20   $124.20  
  Purchase #7 $191.41   9.799%   $210.1663   $210.17   $210.15   $210.20  
  7 purchase totals = $906.89       $996.3521   $996.35   $996.30   $996.40