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 $44.61   4.791%   $46.7473   $46.75   $46.75   $46.70  
  Purchase #2 $24.59   4.164%   $25.6139   $25.61   $25.60   $25.60  
  Purchase #3 $40.90   5.588%   $43.1855   $43.19   $43.20   $43.20  
  Purchase #4 $54.26   4.707%   $56.814   $56.81   $56.80   $56.80  
  Purchase #5 $144.48   12.653%   $162.7611   $162.76   $162.75   $162.80  
  Purchase #6 $114.93   4.681%   $120.3099   $120.31   $120.30   $120.30  
  Purchase #7 $235.82   10.633%   $260.8947   $260.89   $260.90   $260.90  
  7 purchase totals = $659.59       $716.3264   $716.32   $716.30   $716.30