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 $61.79   5.599%   $65.2496   $65.25   $65.25   $65.20  
  Purchase #2 $206.84   10.550%   $228.6616   $228.66   $228.65   $228.70  
  Purchase #3 $76.98   8.265%   $83.3424   $83.34   $83.35   $83.30  
  Purchase #4 $187.58   4.140%   $195.3458   $195.35   $195.35   $195.30  
  Purchase #5 $127.58   9.438%   $139.621   $139.62   $139.60   $139.60  
  Purchase #6 $167.54   9.230%   $183.0039   $183.00   $183.00   $183.00  
  Purchase #7 $63.40   13.573%   $72.0053   $72.01   $72.00   $72.00  
  7 purchase totals = $891.71       $967.2296   $967.23   $967.20   $967.10