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 $238.81   7.183%   $255.9637   $255.96   $255.95   $256.00  
  Purchase #2 $139.31   5.776%   $147.3565   $147.36   $147.35   $147.40  
  Purchase #3 $11.50   7.299%   $12.3394   $12.34   $12.35   $12.30  
  Purchase #4 $45.68   4.831%   $47.8868   $47.89   $47.90   $47.90  
  Purchase #5 $49.28   13.373%   $55.8702   $55.87   $55.85   $55.90  
  Purchase #6 $19.53   7.168%   $20.9299   $20.93   $20.95   $20.90  
  Purchase #7 $60.87   8.432%   $66.0026   $66.00   $66.00   $66.00  
  7 purchase totals = $564.98       $606.3491   $606.35   $606.35   $606.40