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 $199.68   8.126%   $215.906   $215.91   $215.90   $215.90  
  Purchase #2 $85.90   8.402%   $93.1173   $93.12   $93.10   $93.10  
  Purchase #3 $224.36   5.374%   $236.4171   $236.42   $236.40   $236.40  
  Purchase #4 $165.56   10.538%   $183.0067   $183.01   $183.00   $183.00  
  Purchase #5 $26.88   13.628%   $30.5432   $30.54   $30.55   $30.50  
  Purchase #6 $195.68   4.523%   $204.5306   $204.53   $204.55   $204.50  
  Purchase #7 $48.89   11.718%   $54.6189   $54.62   $54.60   $54.60  
  7 purchase totals = $946.95       $1,018.1398   $1,018.15   $1,018.10   $1,018.00