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 $41.63   11.757%   $46.5244   $46.52   $46.50   $46.50  
  Purchase #2 $237.33   8.826%   $258.2767   $258.28   $258.30   $258.30  
  Purchase #3 $197.77   9.790%   $217.1317   $217.13   $217.15   $217.10  
  Purchase #4 $88.75   5.295%   $93.4493   $93.45   $93.45   $93.40  
  Purchase #5 $245.46   4.298%   $256.0099   $256.01   $256.00   $256.00  
  Purchase #6 $13.89   13.783%   $15.8045   $15.80   $15.80   $15.80  
  Purchase #7 $191.55   10.167%   $211.0249   $211.02   $211.00   $211.00  
  7 purchase totals = $1,016.38       $1,098.2214   $1,098.21   $1,098.20   $1,098.10