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 $87.39   7.509%   $93.9521   $93.95   $93.95   $94.00  
  Purchase #2 $145.37   11.824%   $162.5585   $162.56   $162.55   $162.60  
  Purchase #3 $43.38   13.793%   $49.3634   $49.36   $49.35   $49.40  
  Purchase #4 $23.71   3.801%   $24.6112   $24.61   $24.60   $24.60  
  Purchase #5 $184.37   6.818%   $196.9403   $196.94   $196.95   $196.90  
  Purchase #6 $42.34   5.524%   $44.6789   $44.68   $44.70   $44.70  
  Purchase #7 $23.87   13.521%   $27.0975   $27.10   $27.10   $27.10  
  7 purchase totals = $550.43       $599.2019   $599.20   $599.20   $599.30