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 $92.61   6.195%   $98.3472   $98.35   $98.35   $98.30  
  Purchase #2 $245.34   6.722%   $261.8318   $261.83   $261.85   $261.80  
  Purchase #3 $23.44   3.476%   $24.2548   $24.25   $24.25   $24.30  
  Purchase #4 $234.41   9.347%   $256.3203   $256.32   $256.30   $256.30  
  Purchase #5 $213.48   5.160%   $224.4956   $224.50   $224.50   $224.50  
  Purchase #6 $201.31   8.785%   $218.9951   $219.00   $219.00   $219.00  
  Purchase #7 $31.89   6.520%   $33.9692   $33.97   $33.95   $34.00  
  7 purchase totals = $1,042.48       $1,118.2140   $1,118.22   $1,118.20   $1,118.20