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 $49.28   11.559%   $54.9763   $54.98   $55.00   $55.00  
  Purchase #2 $94.80   3.772%   $98.3759   $98.38   $98.40   $98.40  
  Purchase #3 $31.43   11.575%   $35.068   $35.07   $35.05   $35.10  
  Purchase #4 $80.99   13.669%   $92.0605   $92.06   $92.05   $92.10  
  Purchase #5 $170.47   4.430%   $178.0218   $178.02   $178.00   $178.00  
  Purchase #6 $191.65   7.790%   $206.5795   $206.58   $206.60   $206.60  
  Purchase #7 $59.40   13.502%   $67.4202   $67.42   $67.40   $67.40  
  7 purchase totals = $678.02       $732.5022   $732.51   $732.50   $732.60