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 $41.96   11.632%   $46.8408   $46.84   $46.85   $46.80  
  Purchase #2 $135.50   11.188%   $150.6597   $150.66   $150.65   $150.70  
  Purchase #3 $168.54   4.410%   $175.9726   $175.97   $175.95   $176.00  
  Purchase #4 $199.47   12.415%   $224.2342   $224.23   $224.25   $224.20  
  Purchase #5 $163.56   11.394%   $182.196   $182.20   $182.20   $182.20  
  Purchase #6 $234.91   8.746%   $255.4552   $255.46   $255.45   $255.50  
  Purchase #7 $13.38   12.679%   $15.0765   $15.08   $15.10   $15.10  
  7 purchase totals = $957.32       $1,050.4350   $1,050.44   $1,050.45   $1,050.50