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 $246.44   7.803%   $265.6697   $265.67   $265.65   $265.70  
  Purchase #2 $243.80   3.104%   $251.3676   $251.37   $251.35   $251.40  
  Purchase #3 $182.60   6.425%   $194.3321   $194.33   $194.35   $194.30  
  Purchase #4 $20.70   11.861%   $23.1552   $23.16   $23.15   $23.20  
  Purchase #5 $78.96   9.275%   $86.2835   $86.28   $86.30   $86.30  
  Purchase #6 $63.60   7.472%   $68.3522   $68.35   $68.35   $68.40  
  Purchase #7 $8.64   7.202%   $9.2623   $9.26   $9.25   $9.30  
  7 purchase totals = $844.74       $898.4226   $898.42   $898.40   $898.60