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 $208.81   7.362%   $224.1826   $224.18   $224.20   $224.20  
  Purchase #2 $186.84   12.170%   $209.5784   $209.58   $209.60   $209.60  
  Purchase #3 $231.71   8.348%   $251.0532   $251.05   $251.05   $251.10  
  Purchase #4 $44.71   7.503%   $48.0646   $48.06   $48.05   $48.10  
  Purchase #5 $46.46   7.594%   $49.9882   $49.99   $50.00   $50.00  
  Purchase #6 $30.75   11.814%   $34.3828   $34.38   $34.40   $34.40  
  Purchase #7 $208.75   12.233%   $234.2864   $234.29   $234.30   $234.30  
  7 purchase totals = $958.03       $1,051.5362   $1,051.53   $1,051.60   $1,051.70