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 $240.92   11.653%   $268.9944   $268.99   $269.00   $269.00  
  Purchase #2 $172.55   6.612%   $183.959   $183.96   $183.95   $184.00  
  Purchase #3 $86.29   7.634%   $92.8774   $92.88   $92.90   $92.90  
  Purchase #4 $173.30   5.241%   $182.3827   $182.38   $182.40   $182.40  
  Purchase #5 $116.36   11.312%   $129.5226   $129.52   $129.50   $129.50  
  Purchase #6 $27.92   11.567%   $31.1495   $31.15   $31.15   $31.10  
  Purchase #7 $142.86   9.481%   $156.4046   $156.40   $156.40   $156.40  
  7 purchase totals = $960.20       $1,045.2902   $1,045.28   $1,045.30   $1,045.30