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 $8.79   10.662%   $9.7272   $9.73   $9.75   $9.70  
  Purchase #2 $125.99   5.254%   $132.6095   $132.61   $132.60   $132.60  
  Purchase #3 $55.31   6.614%   $58.9682   $58.97   $58.95   $59.00  
  Purchase #4 $205.75   11.558%   $229.5306   $229.53   $229.55   $229.50  
  Purchase #5 $92.65   12.539%   $104.2674   $104.27   $104.25   $104.30  
  Purchase #6 $240.28   11.550%   $268.0323   $268.03   $268.05   $268.00  
  Purchase #7 $150.85   12.619%   $169.8858   $169.89   $169.90   $169.90  
  7 purchase totals = $879.62       $973.0210   $973.03   $973.05   $973.00