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 $16.79   9.303%   $18.352   $18.35   $18.35   $18.40  
  Purchase #2 $82.49   10.765%   $91.37   $91.37   $91.35   $91.40  
  Purchase #3 $101.38   8.359%   $109.8544   $109.85   $109.85   $109.90  
  Purchase #4 $144.86   7.449%   $155.6506   $155.65   $155.65   $155.70  
  Purchase #5 $89.77   13.180%   $101.6017   $101.60   $101.60   $101.60  
  Purchase #6 $179.86   10.857%   $199.3874   $199.39   $199.40   $199.40  
  Purchase #7 $186.25   9.714%   $204.3423   $204.34   $204.35   $204.30  
  7 purchase totals = $801.40       $880.5584   $880.55   $880.55   $880.70