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 $55.91   11.721%   $62.4632   $62.46   $62.45   $62.50  
  Purchase #2 $79.78   8.254%   $86.365   $86.37   $86.35   $86.40  
  Purchase #3 $236.89   6.374%   $251.9894   $251.99   $252.00   $252.00  
  Purchase #4 $33.88   9.824%   $37.2084   $37.21   $37.20   $37.20  
  Purchase #5 $189.31   13.148%   $214.2005   $214.20   $214.20   $214.20  
  Purchase #6 $24.35   3.240%   $25.1389   $25.14   $25.15   $25.10  
  Purchase #7 $20.82   10.508%   $23.0078   $23.01   $23.00   $23.00  
  7 purchase totals = $640.94       $700.3732   $700.38   $700.35   $700.40