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 $244.74   12.670%   $275.7486   $275.75   $275.75   $275.70  
  Purchase #2 $225.43   13.332%   $255.4843   $255.48   $255.50   $255.50  
  Purchase #3 $64.83   13.654%   $73.6819   $73.68   $73.70   $73.70  
  Purchase #4 $161.53   8.672%   $175.5379   $175.54   $175.55   $175.50  
  Purchase #5 $51.56   13.138%   $58.334   $58.33   $58.35   $58.30  
  Purchase #6 $246.35   8.578%   $267.4819   $267.48   $267.50   $267.50  
  Purchase #7 $212.80   13.378%   $241.2684   $241.27   $241.25   $241.30  
  7 purchase totals = $1,207.24       $1,347.5370   $1,347.53   $1,347.60   $1,347.50