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 $225.48   11.753%   $251.9807   $251.98   $252.00   $252.00  
  Purchase #2 $212.87   12.545%   $239.5745   $239.57   $239.55   $239.60  
  Purchase #3 $128.57   8.829%   $139.9214   $139.92   $139.90   $139.90  
  Purchase #4 $87.44   11.625%   $97.6049   $97.60   $97.60   $97.60  
  Purchase #5 $72.46   13.192%   $82.0189   $82.02   $82.00   $82.00  
  Purchase #6 $140.52   13.420%   $159.3778   $159.38   $159.40   $159.40  
  Purchase #7 $39.45   9.797%   $43.3149   $43.31   $43.30   $43.30  
  7 purchase totals = $906.79       $1,013.7931   $1,013.78   $1,013.75   $1,013.80