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 $111.55   11.373%   $124.2366   $124.24   $124.25   $124.20  
  Purchase #2 $55.50   3.469%   $57.4253   $57.43   $57.45   $57.40  
  Purchase #3 $59.29   10.674%   $65.6186   $65.62   $65.60   $65.60  
  Purchase #4 $109.75   6.651%   $117.0495   $117.05   $117.05   $117.00  
  Purchase #5 $227.41   8.449%   $246.6239   $246.62   $246.60   $246.60  
  Purchase #6 $72.60   3.267%   $74.9718   $74.97   $74.95   $75.00  
  Purchase #7 $240.99   8.159%   $260.6524   $260.65   $260.65   $260.70  
  7 purchase totals = $877.09       $946.5781   $946.58   $946.55   $946.50