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 $56.32   8.788%   $61.2694   $61.27   $61.25   $61.30  
  Purchase #2 $152.62   7.321%   $163.7933   $163.79   $163.80   $163.80  
  Purchase #3 $12.45   3.514%   $12.8875   $12.89   $12.90   $12.90  
  Purchase #4 $168.44   3.656%   $174.5982   $174.60   $174.60   $174.60  
  Purchase #5 $98.34   4.250%   $102.5195   $102.52   $102.50   $102.50  
  Purchase #6 $230.96   8.498%   $250.587   $250.59   $250.60   $250.60  
  Purchase #7 $107.52   10.746%   $119.0741   $119.07   $119.05   $119.10  
  7 purchase totals = $826.65       $884.7290   $884.73   $884.70   $884.80