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 $85.57   7.483%   $91.9732   $91.97   $91.95   $92.00  
  Purchase #2 $97.95   7.544%   $105.3393   $105.34   $105.35   $105.30  
  Purchase #3 $232.51   11.858%   $260.081   $260.08   $260.10   $260.10  
  Purchase #4 $23.50   8.538%   $25.5064   $25.51   $25.50   $25.50  
  Purchase #5 $10.43   3.270%   $10.7711   $10.77   $10.75   $10.80  
  Purchase #6 $176.87   3.168%   $182.4732   $182.47   $182.45   $182.50  
  Purchase #7 $111.70   13.641%   $126.937   $126.94   $126.95   $126.90  
  7 purchase totals = $738.53       $803.0812   $803.08   $803.05   $803.10