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 $233.58   12.206%   $262.0908   $262.09   $262.10   $262.10  
  Purchase #2 $247.63   9.442%   $271.0112   $271.01   $271.00   $271.00  
  Purchase #3 $46.93   12.212%   $52.6611   $52.66   $52.65   $52.70  
  Purchase #4 $15.73   8.465%   $17.0615   $17.06   $17.05   $17.10  
  Purchase #5 $54.36   6.666%   $57.9836   $57.98   $58.00   $58.00  
  Purchase #6 $218.44   11.323%   $243.174   $243.17   $243.15   $243.20  
  Purchase #7 $208.97   11.198%   $232.3705   $232.37   $232.35   $232.40  
  7 purchase totals = $1,025.64       $1,136.3527   $1,136.34   $1,136.30   $1,136.50