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 $244.62   10.856%   $271.1759   $271.18   $271.20   $271.20  
  Purchase #2 $108.64   11.214%   $120.8229   $120.82   $120.80   $120.80  
  Purchase #3 $50.37   10.350%   $55.5833   $55.58   $55.60   $55.60  
  Purchase #4 $53.76   6.300%   $57.1469   $57.15   $57.15   $57.10  
  Purchase #5 $105.25   5.399%   $110.9324   $110.93   $110.95   $110.90  
  Purchase #6 $163.47   6.849%   $174.6661   $174.67   $174.65   $174.70  
  Purchase #7 $224.90   8.571%   $244.1762   $244.18   $244.20   $244.20  
  7 purchase totals = $951.01       $1,034.5037   $1,034.51   $1,034.55   $1,034.50