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 $22.48   6.623%   $23.9689   $23.97   $23.95   $24.00  
  Purchase #2 $101.48   6.133%   $107.7038   $107.70   $107.70   $107.70  
  Purchase #3 $184.87   4.102%   $192.4534   $192.45   $192.45   $192.50  
  Purchase #4 $104.34   6.707%   $111.3381   $111.34   $111.35   $111.30  
  Purchase #5 $32.38   8.245%   $35.0497   $35.05   $35.05   $35.00  
  Purchase #6 $212.40   3.253%   $219.3094   $219.31   $219.30   $219.30  
  Purchase #7 $153.89   5.133%   $161.7892   $161.79   $161.80   $161.80  
  7 purchase totals = $811.84       $851.6125   $851.61   $851.60   $851.60