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 $71.37   6.753%   $76.1896   $76.19   $76.20   $76.20  
  Purchase #2 $125.42   7.845%   $135.2592   $135.26   $135.25   $135.30  
  Purchase #3 $84.65   7.601%   $91.0842   $91.08   $91.10   $91.10  
  Purchase #4 $97.71   13.603%   $111.0015   $111.00   $111.00   $111.00  
  Purchase #5 $188.42   10.324%   $207.8725   $207.87   $207.85   $207.90  
  Purchase #6 $22.47   11.359%   $25.0224   $25.02   $25.00   $25.00  
  Purchase #7 $220.64   3.448%   $228.2477   $228.25   $228.25   $228.20  
  7 purchase totals = $810.68       $874.6771   $874.67   $874.65   $874.70