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 $236.26   12.414%   $265.5893   $265.59   $265.60   $265.60  
  Purchase #2 $135.83   9.616%   $148.8914   $148.89   $148.90   $148.90  
  Purchase #3 $217.26   6.733%   $231.8881   $231.89   $231.90   $231.90  
  Purchase #4 $153.53   7.540%   $165.1062   $165.11   $165.10   $165.10  
  Purchase #5 $14.65   11.348%   $16.3125   $16.31   $16.30   $16.30  
  Purchase #6 $241.49   9.219%   $263.753   $263.75   $263.75   $263.80  
  Purchase #7 $157.42   8.759%   $171.2084   $171.21   $171.20   $171.20  
  7 purchase totals = $1,156.44       $1,262.7489   $1,262.75   $1,262.75   $1,262.80