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 $210.55   13.465%   $238.9006   $238.90   $238.90   $238.90  
  Purchase #2 $131.39   8.830%   $142.9917   $142.99   $143.00   $143.00  
  Purchase #3 $204.96   9.747%   $224.9375   $224.94   $224.95   $224.90  
  Purchase #4 $46.78   10.473%   $51.6793   $51.68   $51.70   $51.70  
  Purchase #5 $86.95   6.123%   $92.2739   $92.27   $92.25   $92.30  
  Purchase #6 $144.39   6.822%   $154.2403   $154.24   $154.25   $154.20  
  Purchase #7 $163.65   7.587%   $176.0661   $176.07   $176.05   $176.10  
  7 purchase totals = $988.67       $1,081.0894   $1,081.09   $1,081.10   $1,081.10