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 $33.98   8.297%   $36.7993   $36.80   $36.80   $36.80  
  Purchase #2 $182.63   11.456%   $203.5521   $203.55   $203.55   $203.60  
  Purchase #3 $230.34   12.175%   $258.3839   $258.38   $258.40   $258.40  
  Purchase #4 $48.57   12.603%   $54.6913   $54.69   $54.70   $54.70  
  Purchase #5 $63.81   6.752%   $68.1185   $68.12   $68.10   $68.10  
  Purchase #6 $101.39   4.747%   $106.203   $106.20   $106.20   $106.20  
  Purchase #7 $217.40   10.735%   $240.7379   $240.74   $240.75   $240.70  
  7 purchase totals = $878.12       $968.4860   $968.48   $968.50   $968.50