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 $60.88   12.209%   $68.3128   $68.31   $68.30   $68.30  
  Purchase #2 $45.47   12.861%   $51.3179   $51.32   $51.30   $51.30  
  Purchase #3 $124.63   13.394%   $141.3229   $141.32   $141.30   $141.30  
  Purchase #4 $250.92   9.332%   $274.3359   $274.34   $274.35   $274.30  
  Purchase #5 $61.99   7.494%   $66.6355   $66.64   $66.65   $66.60  
  Purchase #6 $169.66   8.439%   $183.9776   $183.98   $184.00   $184.00  
  Purchase #7 $5.88   7.553%   $6.3241   $6.32   $6.30   $6.30  
  7 purchase totals = $719.43       $792.2267   $792.23   $792.20   $792.10