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 $61.28   10.599%   $67.7751   $67.78   $67.80   $67.80  
  Purchase #2 $70.77   8.687%   $76.9178   $76.92   $76.90   $76.90  
  Purchase #3 $58.40   5.282%   $61.4847   $61.48   $61.50   $61.50  
  Purchase #4 $203.83   3.562%   $211.0904   $211.09   $211.10   $211.10  
  Purchase #5 $103.80   3.204%   $107.1258   $107.13   $107.15   $107.10  
  Purchase #6 $248.97   3.309%   $257.2084   $257.21   $257.20   $257.20  
  Purchase #7 $205.92   3.569%   $213.2693   $213.27   $213.25   $213.30  
  7 purchase totals = $952.97       $994.8715   $994.88   $994.90   $994.90