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 $211.94   6.412%   $225.5296   $225.53   $225.55   $225.50  
  Purchase #2 $119.42   4.580%   $124.8894   $124.89   $124.90   $124.90  
  Purchase #3 $73.66   7.126%   $78.909   $78.91   $78.90   $78.90  
  Purchase #4 $209.33   11.181%   $232.7352   $232.74   $232.75   $232.70  
  Purchase #5 $161.25   13.142%   $182.4415   $182.44   $182.45   $182.40  
  Purchase #6 $23.52   11.308%   $26.1796   $26.18   $26.20   $26.20  
  Purchase #7 $161.66   13.473%   $183.4405   $183.44   $183.45   $183.40  
  7 purchase totals = $960.78       $1,054.1248   $1,054.13   $1,054.20   $1,054.00