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 $58.96   10.159%   $64.9497   $64.95   $64.95   $64.90  
  Purchase #2 $200.43   8.765%   $217.9977   $218.00   $218.00   $218.00  
  Purchase #3 $230.28   5.488%   $242.9178   $242.92   $242.90   $242.90  
  Purchase #4 $187.82   13.319%   $212.8357   $212.84   $212.85   $212.80  
  Purchase #5 $212.48   11.646%   $237.2254   $237.23   $237.25   $237.20  
  Purchase #6 $203.93   9.697%   $223.7051   $223.71   $223.70   $223.70  
  Purchase #7 $165.63   12.750%   $186.7478   $186.75   $186.75   $186.70  
  7 purchase totals = $1,259.53       $1,386.3792   $1,386.40   $1,386.40   $1,386.20