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 $236.66   13.805%   $269.3309   $269.33   $269.35   $269.30  
  Purchase #2 $144.38   8.163%   $156.1657   $156.17   $156.15   $156.20  
  Purchase #3 $187.67   10.224%   $206.8574   $206.86   $206.85   $206.90  
  Purchase #4 $197.40   11.833%   $220.7583   $220.76   $220.75   $220.80  
  Purchase #5 $129.63   7.684%   $139.5908   $139.59   $139.60   $139.60  
  Purchase #6 $40.25   9.209%   $43.9566   $43.96   $43.95   $44.00  
  Purchase #7 $21.27   10.249%   $23.45   $23.45   $23.45   $23.50  
  7 purchase totals = $957.26       $1,060.1097   $1,060.12   $1,060.10   $1,060.30