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 $207.81   4.548%   $217.2612   $217.26   $217.25   $217.30  
  Purchase #2 $66.97   13.496%   $76.0083   $76.01   $76.00   $76.00  
  Purchase #3 $20.87   13.348%   $23.6557   $23.66   $23.65   $23.70  
  Purchase #4 $174.85   13.337%   $198.1697   $198.17   $198.15   $198.20  
  Purchase #5 $67.92   6.818%   $72.5508   $72.55   $72.55   $72.60  
  Purchase #6 $90.45   12.352%   $101.6224   $101.62   $101.60   $101.60  
  Purchase #7 $210.80   12.102%   $236.311   $236.31   $236.30   $236.30  
  7 purchase totals = $839.67       $925.5791   $925.58   $925.50   $925.70