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 $54.67   10.593%   $60.4612   $60.46   $60.45   $60.50  
  Purchase #2 $178.84   11.751%   $199.8555   $199.86   $199.85   $199.90  
  Purchase #3 $62.87   4.308%   $65.5784   $65.58   $65.60   $65.60  
  Purchase #4 $32.67   6.570%   $34.8164   $34.82   $34.80   $34.80  
  Purchase #5 $218.89   6.690%   $233.5337   $233.53   $233.55   $233.50  
  Purchase #6 $224.67   10.408%   $248.0537   $248.05   $248.05   $248.10  
  Purchase #7 $13.41   6.553%   $14.2888   $14.29   $14.30   $14.30  
  7 purchase totals = $786.02       $856.5877   $856.59   $856.60   $856.70