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 $247.61   6.331%   $263.2862   $263.29   $263.30   $263.30  
  Purchase #2 $58.41   8.812%   $63.5571   $63.56   $63.55   $63.60  
  Purchase #3 $137.60   6.246%   $146.1945   $146.19   $146.20   $146.20  
  Purchase #4 $71.98   5.254%   $75.7618   $75.76   $75.75   $75.80  
  Purchase #5 $186.67   7.497%   $200.6646   $200.66   $200.65   $200.70  
  Purchase #6 $151.64   6.331%   $161.2403   $161.24   $161.25   $161.20  
  Purchase #7 $74.34   3.843%   $77.1969   $77.20   $77.20   $77.20  
  7 purchase totals = $928.25       $987.9014   $987.90   $987.90   $988.00