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 $94.60   5.726%   $100.0168   $100.02   $100.00   $100.00  
  Purchase #2 $185.61   8.213%   $200.8541   $200.85   $200.85   $200.90  
  Purchase #3 $242.45   10.494%   $267.8927   $267.89   $267.90   $267.90  
  Purchase #4 $222.64   5.231%   $234.2863   $234.29   $234.30   $234.30  
  Purchase #5 $87.32   7.566%   $93.9266   $93.93   $93.95   $93.90  
  Purchase #6 $240.42   11.690%   $268.5251   $268.53   $268.55   $268.50  
  Purchase #7 $76.35   7.276%   $81.9052   $81.91   $81.90   $81.90  
  7 purchase totals = $1,149.39       $1,247.4068   $1,247.42   $1,247.45   $1,247.40