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 $33.63   4.310%   $35.0795   $35.08   $35.10   $35.10  
  Purchase #2 $231.58   7.519%   $248.9925   $248.99   $249.00   $249.00  
  Purchase #3 $49.29   6.515%   $52.5012   $52.50   $52.50   $52.50  
  Purchase #4 $250.86   4.388%   $261.8677   $261.87   $261.85   $261.90  
  Purchase #5 $121.92   6.307%   $129.6095   $129.61   $129.60   $129.60  
  Purchase #6 $88.59   12.730%   $99.8675   $99.87   $99.85   $99.90  
  Purchase #7 $245.72   12.855%   $277.3073   $277.31   $277.30   $277.30  
  7 purchase totals = $1,021.59       $1,105.2252   $1,105.23   $1,105.20   $1,105.30