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 $229.77   13.637%   $261.1037   $261.10   $261.10   $261.10  
  Purchase #2 $156.53   9.554%   $171.4849   $171.48   $171.50   $171.50  
  Purchase #3 $160.29   8.124%   $173.312   $173.31   $173.30   $173.30  
  Purchase #4 $238.39   9.373%   $260.7343   $260.73   $260.75   $260.70  
  Purchase #5 $239.82   5.345%   $252.6384   $252.64   $252.65   $252.60  
  Purchase #6 $41.84   6.140%   $44.409   $44.41   $44.40   $44.40  
  Purchase #7 $226.25   10.162%   $249.2415   $249.24   $249.25   $249.20  
  7 purchase totals = $1,292.89       $1,412.9238   $1,412.91   $1,412.95   $1,412.80