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 $60.59   10.480%   $66.9398   $66.94   $66.95   $66.90  
  Purchase #2 $225.53   10.813%   $249.9166   $249.92   $249.90   $249.90  
  Purchase #3 $228.82   13.339%   $259.3423   $259.34   $259.35   $259.30  
  Purchase #4 $36.27   12.512%   $40.8081   $40.81   $40.80   $40.80  
  Purchase #5 $132.97   13.629%   $151.0925   $151.09   $151.10   $151.10  
  Purchase #6 $24.53   6.133%   $26.0344   $26.03   $26.05   $26.00  
  Purchase #7 $143.49   8.153%   $155.1887   $155.19   $155.20   $155.20  
  7 purchase totals = $852.20       $949.3224   $949.32   $949.35   $949.20