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 $84.34   9.362%   $92.2359   $92.24   $92.25   $92.20  
  Purchase #2 $155.87   12.185%   $174.8628   $174.86   $174.85   $174.90  
  Purchase #3 $239.71   4.331%   $250.0918   $250.09   $250.10   $250.10  
  Purchase #4 $74.79   3.532%   $77.4316   $77.43   $77.45   $77.40  
  Purchase #5 $184.96   13.754%   $210.3994   $210.40   $210.40   $210.40  
  Purchase #6 $179.90   8.299%   $194.8299   $194.83   $194.85   $194.80  
  Purchase #7 $221.73   5.241%   $233.3509   $233.35   $233.35   $233.40  
  7 purchase totals = $1,141.30       $1,233.2023   $1,233.20   $1,233.25   $1,233.20