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 $242.43   13.829%   $275.9556   $275.96   $275.95   $276.00  
  Purchase #2 $136.67   12.662%   $153.9752   $153.98   $154.00   $154.00  
  Purchase #3 $241.61   10.836%   $267.7909   $267.79   $267.80   $267.80  
  Purchase #4 $225.84   5.260%   $237.7192   $237.72   $237.70   $237.70  
  Purchase #5 $53.32   4.298%   $55.6117   $55.61   $55.60   $55.60  
  Purchase #6 $126.74   10.231%   $139.7068   $139.71   $139.70   $139.70  
  Purchase #7 $180.88   10.653%   $200.1491   $200.15   $200.15   $200.10  
  7 purchase totals = $1,207.49       $1,330.9085   $1,330.92   $1,330.90   $1,330.90