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 $203.78   4.405%   $212.7565   $212.76   $212.75   $212.80  
  Purchase #2 $242.98   9.536%   $266.1506   $266.15   $266.15   $266.20  
  Purchase #3 $180.55   5.377%   $190.2582   $190.26   $190.25   $190.30  
  Purchase #4 $62.91   3.109%   $64.8659   $64.87   $64.85   $64.90  
  Purchase #5 $161.62   11.868%   $180.8011   $180.80   $180.80   $180.80  
  Purchase #6 $69.50   10.572%   $76.8475   $76.85   $76.85   $76.80  
  Purchase #7 $220.60   13.710%   $250.8443   $250.84   $250.85   $250.80  
  7 purchase totals = $1,141.94       $1,242.5241   $1,242.53   $1,242.50   $1,242.60