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 $96.67   6.562%   $103.0135   $103.01   $103.00   $103.00  
  Purchase #2 $247.92   4.620%   $259.3739   $259.37   $259.35   $259.40  
  Purchase #3 $168.47   11.224%   $187.3791   $187.38   $187.40   $187.40  
  Purchase #4 $143.89   11.478%   $160.4057   $160.41   $160.40   $160.40  
  Purchase #5 $215.32   7.451%   $231.3635   $231.36   $231.35   $231.40  
  Purchase #6 $250.27   12.734%   $282.1394   $282.14   $282.15   $282.10  
  Purchase #7 $177.29   8.703%   $192.7195   $192.72   $192.70   $192.70  
  7 purchase totals = $1,299.83       $1,416.3946   $1,416.39   $1,416.35   $1,416.40