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 $234.25   13.136%   $265.0211   $265.02   $265.00   $265.00  
  Purchase #2 $190.28   3.333%   $196.622   $196.62   $196.60   $196.60  
  Purchase #3 $154.67   7.185%   $165.783   $165.78   $165.80   $165.80  
  Purchase #4 $189.94   8.306%   $205.7164   $205.72   $205.70   $205.70  
  Purchase #5 $58.59   7.482%   $62.9737   $62.97   $62.95   $63.00  
  Purchase #6 $85.66   6.519%   $91.2442   $91.24   $91.25   $91.20  
  Purchase #7 $112.48   5.711%   $118.9037   $118.90   $118.90   $118.90  
  7 purchase totals = $1,025.87       $1,106.2641   $1,106.25   $1,106.20   $1,106.20