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 $143.83   6.549%   $153.2494   $153.25   $153.25   $153.20  
  Purchase #2 $59.64   4.256%   $62.1783   $62.18   $62.20   $62.20  
  Purchase #3 $201.29   8.450%   $218.299   $218.30   $218.30   $218.30  
  Purchase #4 $48.36   8.233%   $52.3415   $52.34   $52.35   $52.30  
  Purchase #5 $236.96   3.575%   $245.4313   $245.43   $245.45   $245.40  
  Purchase #6 $154.91   8.592%   $168.2199   $168.22   $168.20   $168.20  
  Purchase #7 $69.36   11.671%   $77.455   $77.46   $77.45   $77.50  
  7 purchase totals = $914.35       $977.1744   $977.18   $977.20   $977.10