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 $185.26   13.646%   $210.5406   $210.54   $210.55   $210.50  
  Purchase #2 $240.96   9.425%   $263.6705   $263.67   $263.65   $263.70  
  Purchase #3 $78.85   4.337%   $82.2697   $82.27   $82.25   $82.30  
  Purchase #4 $211.92   10.699%   $234.5933   $234.59   $234.60   $234.60  
  Purchase #5 $224.73   7.465%   $241.5061   $241.51   $241.50   $241.50  
  Purchase #6 $157.95   6.735%   $168.5879   $168.59   $168.60   $168.60  
  Purchase #7 $129.66   8.493%   $140.672   $140.67   $140.65   $140.70  
  7 purchase totals = $1,229.33       $1,341.8401   $1,341.84   $1,341.80   $1,341.90