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 $230.96   13.723%   $262.6546   $262.65   $262.65   $262.70  
  Purchase #2 $210.81   13.634%   $239.5518   $239.55   $239.55   $239.60  
  Purchase #3 $24.80   13.325%   $28.1046   $28.10   $28.10   $28.10  
  Purchase #4 $126.39   13.450%   $143.3895   $143.39   $143.40   $143.40  
  Purchase #5 $98.89   5.727%   $104.5534   $104.55   $104.55   $104.60  
  Purchase #6 $69.33   11.769%   $77.4894   $77.49   $77.50   $77.50  
  Purchase #7 $119.33   8.532%   $129.5112   $129.51   $129.50   $129.50  
  7 purchase totals = $880.51       $985.2545   $985.24   $985.25   $985.40