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 $25.89   4.358%   $27.0183   $27.02   $27.00   $27.00  
  Purchase #2 $128.39   11.108%   $142.6516   $142.65   $142.65   $142.70  
  Purchase #3 $62.78   8.722%   $68.2557   $68.26   $68.25   $68.30  
  Purchase #4 $241.31   6.578%   $257.1834   $257.18   $257.20   $257.20  
  Purchase #5 $247.71   8.377%   $268.4607   $268.46   $268.45   $268.50  
  Purchase #6 $193.53   12.194%   $217.129   $217.13   $217.15   $217.10  
  Purchase #7 $67.77   6.302%   $72.0409   $72.04   $72.05   $72.00  
  7 purchase totals = $967.38       $1,052.7396   $1,052.74   $1,052.75   $1,052.80