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 $57.41   9.416%   $62.8157   $62.82   $62.80   $62.80  
  Purchase #2 $111.99   3.817%   $116.2647   $116.26   $116.25   $116.30  
  Purchase #3 $195.39   10.643%   $216.1854   $216.19   $216.20   $216.20  
  Purchase #4 $151.70   6.295%   $161.2495   $161.25   $161.25   $161.20  
  Purchase #5 $150.88   10.724%   $167.0604   $167.06   $167.05   $167.10  
  Purchase #6 $9.52   5.143%   $10.0096   $10.01   $10.00   $10.00  
  Purchase #7 $218.72   5.321%   $230.3581   $230.36   $230.35   $230.40  
  7 purchase totals = $895.61       $963.9434   $963.95   $963.90   $964.00