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 $224.51   5.524%   $236.9119   $236.91   $236.90   $236.90  
  Purchase #2 $150.26   5.385%   $158.3515   $158.35   $158.35   $158.40  
  Purchase #3 $202.36   8.501%   $219.5626   $219.56   $219.55   $219.60  
  Purchase #4 $148.83   6.758%   $158.8879   $158.89   $158.90   $158.90  
  Purchase #5 $217.38   5.758%   $229.8967   $229.90   $229.90   $229.90  
  Purchase #6 $25.81   5.857%   $27.3217   $27.32   $27.30   $27.30  
  Purchase #7 $197.37   6.411%   $210.0234   $210.02   $210.00   $210.00  
  7 purchase totals = $1,166.52       $1,240.9557   $1,240.95   $1,240.90   $1,241.00