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 $215.52   13.417%   $244.4363   $244.44   $244.45   $244.40  
  Purchase #2 $7.81   3.357%   $8.0722   $8.07   $8.05   $8.10  
  Purchase #3 $42.29   12.569%   $47.6054   $47.61   $47.60   $47.60  
  Purchase #4 $25.35   3.666%   $26.2793   $26.28   $26.30   $26.30  
  Purchase #5 $196.55   3.371%   $203.1757   $203.18   $203.20   $203.20  
  Purchase #6 $126.93   4.468%   $132.6012   $132.60   $132.60   $132.60  
  Purchase #7 $144.32   11.567%   $161.0135   $161.01   $161.00   $161.00  
  7 purchase totals = $758.77       $823.1836   $823.19   $823.20   $823.20