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 $87.74   6.585%   $93.5177   $93.52   $93.50   $93.50  
  Purchase #2 $191.33   9.163%   $208.8616   $208.86   $208.85   $208.90  
  Purchase #3 $8.85   12.167%   $9.9268   $9.93   $9.95   $9.90  
  Purchase #4 $68.47   12.801%   $77.2348   $77.23   $77.25   $77.20  
  Purchase #5 $184.49   8.328%   $199.8543   $199.85   $199.85   $199.90  
  Purchase #6 $96.34   6.117%   $102.2331   $102.23   $102.25   $102.20  
  Purchase #7 $19.73   13.241%   $22.3424   $22.34   $22.35   $22.30  
  7 purchase totals = $656.95       $713.9707   $713.96   $714.00   $713.90