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 $32.31   8.172%   $34.9504   $34.95   $34.95   $35.00  
  Purchase #2 $232.53   6.872%   $248.5095   $248.51   $248.50   $248.50  
  Purchase #3 $226.95   4.738%   $237.7029   $237.70   $237.70   $237.70  
  Purchase #4 $87.56   5.339%   $92.2348   $92.23   $92.25   $92.20  
  Purchase #5 $8.97   12.697%   $10.1089   $10.11   $10.10   $10.10  
  Purchase #6 $203.85   11.259%   $226.8015   $226.80   $226.80   $226.80  
  Purchase #7 $230.86   10.267%   $254.5624   $254.56   $254.55   $254.60  
  7 purchase totals = $1,023.03       $1,104.8704   $1,104.86   $1,104.85   $1,104.90