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 $58.71   11.294%   $65.3407   $65.34   $65.35   $65.30  
  Purchase #2 $82.57   13.189%   $93.4602   $93.46   $93.45   $93.50  
  Purchase #3 $82.64   5.871%   $87.4918   $87.49   $87.50   $87.50  
  Purchase #4 $30.96   6.152%   $32.8647   $32.86   $32.85   $32.90  
  Purchase #5 $231.64   9.535%   $253.7269   $253.73   $253.75   $253.70  
  Purchase #6 $88.48   5.373%   $93.234   $93.23   $93.25   $93.20  
  Purchase #7 $57.81   5.279%   $60.8618   $60.86   $60.85   $60.90  
  7 purchase totals = $632.81       $686.9801   $686.97   $687.00   $687.00