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 $201.53   11.179%   $224.059   $224.06   $224.05   $224.10  
  Purchase #2 $136.38   11.660%   $152.2819   $152.28   $152.30   $152.30  
  Purchase #3 $116.70   13.745%   $132.7404   $132.74   $132.75   $132.70  
  Purchase #4 $169.65   11.664%   $189.438   $189.44   $189.45   $189.40  
  Purchase #5 $52.28   12.521%   $58.826   $58.83   $58.85   $58.80  
  Purchase #6 $53.96   3.168%   $55.6695   $55.67   $55.65   $55.70  
  Purchase #7 $144.32   11.535%   $160.9673   $160.97   $160.95   $161.00  
  7 purchase totals = $874.82       $973.9821   $973.99   $974.00   $974.00