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 $131.49   7.494%   $141.3439   $141.34   $141.35   $141.30  
  Purchase #2 $185.49   13.597%   $210.7111   $210.71   $210.70   $210.70  
  Purchase #3 $11.88   10.662%   $13.1466   $13.15   $13.15   $13.10  
  Purchase #4 $39.62   6.529%   $42.2068   $42.21   $42.20   $42.20  
  Purchase #5 $157.25   7.777%   $169.4793   $169.48   $169.50   $169.50  
  Purchase #6 $177.47   9.118%   $193.6517   $193.65   $193.65   $193.70  
  Purchase #7 $241.48   4.358%   $252.0037   $252.00   $252.00   $252.00  
  7 purchase totals = $944.68       $1,022.5431   $1,022.54   $1,022.55   $1,022.50