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 $218.50   13.149%   $247.2306   $247.23   $247.25   $247.20  
  Purchase #2 $169.82   3.361%   $175.5277   $175.53   $175.55   $175.50  
  Purchase #3 $88.48   10.632%   $97.8872   $97.89   $97.90   $97.90  
  Purchase #4 $23.71   10.824%   $26.2764   $26.28   $26.30   $26.30  
  Purchase #5 $186.83   7.592%   $201.0141   $201.01   $201.00   $201.00  
  Purchase #6 $216.34   11.644%   $241.5306   $241.53   $241.55   $241.50  
  Purchase #7 $83.27   12.170%   $93.404   $93.40   $93.40   $93.40  
  7 purchase totals = $986.95       $1,082.8706   $1,082.87   $1,082.95   $1,082.80