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 $108.84   9.794%   $119.4998   $119.50   $119.50   $119.50  
  Purchase #2 $83.57   4.551%   $87.3733   $87.37   $87.35   $87.40  
  Purchase #3 $35.37   3.501%   $36.6083   $36.61   $36.60   $36.60  
  Purchase #4 $117.49   3.545%   $121.655   $121.66   $121.65   $121.70  
  Purchase #5 $236.51   7.735%   $254.804   $254.80   $254.80   $254.80  
  Purchase #6 $82.32   10.180%   $90.7002   $90.70   $90.70   $90.70  
  Purchase #7 $232.29   4.525%   $242.8011   $242.80   $242.80   $242.80  
  7 purchase totals = $896.39       $953.4417   $953.44   $953.40   $953.50