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 $83.57   10.867%   $92.6516   $92.65   $92.65   $92.70  
  Purchase #2 $217.43   11.391%   $242.1975   $242.20   $242.20   $242.20  
  Purchase #3 $169.36   5.418%   $178.5359   $178.54   $178.55   $178.50  
  Purchase #4 $105.63   11.528%   $117.807   $117.81   $117.80   $117.80  
  Purchase #5 $7.33   3.354%   $7.5758   $7.58   $7.60   $7.60  
  Purchase #6 $107.25   13.609%   $121.8457   $121.85   $121.85   $121.80  
  Purchase #7 $44.98   3.873%   $46.7221   $46.72   $46.70   $46.70  
  7 purchase totals = $735.55       $807.3356   $807.35   $807.35   $807.30