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 $58.99   6.837%   $63.0231   $63.02   $63.00   $63.00  
  Purchase #2 $12.34   13.798%   $14.0427   $14.04   $14.05   $14.00  
  Purchase #3 $169.98   11.596%   $189.6909   $189.69   $189.70   $189.70  
  Purchase #4 $248.33   13.192%   $281.0897   $281.09   $281.10   $281.10  
  Purchase #5 $32.69   6.333%   $34.7603   $34.76   $34.75   $34.80  
  Purchase #6 $119.96   10.811%   $132.9289   $132.93   $132.95   $132.90  
  Purchase #7 $221.59   6.193%   $235.3131   $235.31   $235.30   $235.30  
  7 purchase totals = $863.88       $950.8487   $950.84   $950.85   $950.80