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 $249.99   5.274%   $263.1745   $263.17   $263.15   $263.20  
  Purchase #2 $15.26   11.409%   $17.001   $17.00   $17.00   $17.00  
  Purchase #3 $214.75   6.698%   $229.134   $229.13   $229.15   $229.10  
  Purchase #4 $86.82   13.580%   $98.6102   $98.61   $98.60   $98.60  
  Purchase #5 $231.35   6.363%   $246.0708   $246.07   $246.05   $246.10  
  Purchase #6 $84.60   8.842%   $92.0803   $92.08   $92.10   $92.10  
  Purchase #7 $228.84   7.573%   $246.1701   $246.17   $246.15   $246.20  
  7 purchase totals = $1,111.61       $1,192.2409   $1,192.23   $1,192.20   $1,192.30