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 $26.35   7.766%   $28.3963   $28.40   $28.40   $28.40  
  Purchase #2 $240.78   11.116%   $267.5451   $267.55   $267.55   $267.50  
  Purchase #3 $84.69   13.337%   $95.9851   $95.99   $96.00   $96.00  
  Purchase #4 $53.82   3.862%   $55.8985   $55.90   $55.90   $55.90  
  Purchase #5 $135.61   13.561%   $154.0001   $154.00   $154.00   $154.00  
  Purchase #6 $176.31   13.285%   $199.7328   $199.73   $199.75   $199.70  
  Purchase #7 $215.53   4.148%   $224.4702   $224.47   $224.45   $224.50  
  7 purchase totals = $933.09       $1,026.0281   $1,026.04   $1,026.05   $1,026.00