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 $239.68   8.680%   $260.4842   $260.48   $260.50   $260.50  
  Purchase #2 $52.58   12.762%   $59.2903   $59.29   $59.30   $59.30  
  Purchase #3 $91.64   8.768%   $99.675   $99.68   $99.70   $99.70  
  Purchase #4 $169.87   5.148%   $178.6149   $178.61   $178.60   $178.60  
  Purchase #5 $138.32   10.347%   $152.632   $152.63   $152.65   $152.60  
  Purchase #6 $183.30   11.664%   $204.6801   $204.68   $204.70   $204.70  
  Purchase #7 $68.80   7.789%   $74.1588   $74.16   $74.15   $74.20  
  7 purchase totals = $944.19       $1,029.5353   $1,029.53   $1,029.60   $1,029.60