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 $187.52   4.249%   $195.4877   $195.49   $195.50   $195.50  
  Purchase #2 $220.56   11.746%   $246.467   $246.47   $246.45   $246.50  
  Purchase #3 $26.40   11.721%   $29.4943   $29.49   $29.50   $29.50  
  Purchase #4 $7.60   8.369%   $8.236   $8.24   $8.25   $8.20  
  Purchase #5 $161.91   9.853%   $177.863   $177.86   $177.85   $177.90  
  Purchase #6 $8.97   8.267%   $9.7115   $9.71   $9.70   $9.70  
  Purchase #7 $57.67   12.598%   $64.9353   $64.94   $64.95   $64.90  
  7 purchase totals = $670.63       $732.1948   $732.20   $732.20   $732.20