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 $118.53   3.593%   $122.7888   $122.79   $122.80   $122.80  
  Purchase #2 $192.78   6.163%   $204.661   $204.66   $204.65   $204.70  
  Purchase #3 $85.48   8.627%   $92.8544   $92.85   $92.85   $92.90  
  Purchase #4 $115.61   9.653%   $126.7698   $126.77   $126.75   $126.80  
  Purchase #5 $54.34   13.147%   $61.4841   $61.48   $61.50   $61.50  
  Purchase #6 $196.91   5.592%   $207.9212   $207.92   $207.90   $207.90  
  Purchase #7 $125.68   7.513%   $135.1223   $135.12   $135.10   $135.10  
  7 purchase totals = $889.33       $951.6016   $951.59   $951.55   $951.70