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 $37.96   8.807%   $41.3031   $41.30   $41.30   $41.30  
  Purchase #2 $249.96   12.685%   $281.6674   $281.67   $281.65   $281.70  
  Purchase #3 $196.75   3.862%   $204.3485   $204.35   $204.35   $204.30  
  Purchase #4 $206.49   4.315%   $215.4   $215.40   $215.40   $215.40  
  Purchase #5 $206.97   6.272%   $219.9512   $219.95   $219.95   $220.00  
  Purchase #6 $42.27   5.675%   $44.6688   $44.67   $44.65   $44.70  
  Purchase #7 $215.63   7.428%   $231.647   $231.65   $231.65   $231.60  
  7 purchase totals = $1,156.03       $1,238.9860   $1,238.99   $1,238.95   $1,239.00