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 $85.92   12.278%   $96.4693   $96.47   $96.45   $96.50  
  Purchase #2 $199.91   3.366%   $206.639   $206.64   $206.65   $206.60  
  Purchase #3 $57.79   7.461%   $62.1017   $62.10   $62.10   $62.10  
  Purchase #4 $65.92   6.452%   $70.1732   $70.17   $70.15   $70.20  
  Purchase #5 $74.33   11.562%   $82.924   $82.92   $82.90   $82.90  
  Purchase #6 $52.38   7.127%   $56.1131   $56.11   $56.10   $56.10  
  Purchase #7 $211.51   8.730%   $229.9748   $229.97   $229.95   $230.00  
  7 purchase totals = $747.76       $804.3951   $804.38   $804.30   $804.40