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 $242.78   5.203%   $255.4118   $255.41   $255.40   $255.40  
  Purchase #2 $215.30   13.761%   $244.9274   $244.93   $244.95   $244.90  
  Purchase #3 $26.52   10.490%   $29.3019   $29.30   $29.30   $29.30  
  Purchase #4 $234.97   3.155%   $242.3833   $242.38   $242.40   $242.40  
  Purchase #5 $24.31   9.192%   $26.5446   $26.54   $26.55   $26.50  
  Purchase #6 $103.98   11.232%   $115.659   $115.66   $115.65   $115.70  
  Purchase #7 $117.27   10.166%   $129.1917   $129.19   $129.20   $129.20  
  7 purchase totals = $965.13       $1,043.4197   $1,043.41   $1,043.45   $1,043.40