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 $61.29   7.455%   $65.8592   $65.86   $65.85   $65.90  
  Purchase #2 $108.92   11.363%   $121.2966   $121.30   $121.30   $121.30  
  Purchase #3 $5.78   3.468%   $5.9805   $5.98   $6.00   $6.00  
  Purchase #4 $249.34   9.474%   $272.9625   $272.96   $272.95   $273.00  
  Purchase #5 $171.48   9.758%   $188.213   $188.21   $188.20   $188.20  
  Purchase #6 $239.66   13.494%   $271.9997   $272.00   $272.00   $272.00  
  Purchase #7 $113.85   5.304%   $119.8886   $119.89   $119.90   $119.90  
  7 purchase totals = $950.32       $1,046.2001   $1,046.20   $1,046.20   $1,046.30