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 $234.31   12.304%   $263.1395   $263.14   $263.15   $263.10  
  Purchase #2 $142.34   4.437%   $148.6556   $148.66   $148.65   $148.70  
  Purchase #3 $188.76   13.531%   $214.3011   $214.30   $214.30   $214.30  
  Purchase #4 $59.40   4.386%   $62.0053   $62.01   $62.00   $62.00  
  Purchase #5 $186.45   4.640%   $195.1013   $195.10   $195.10   $195.10  
  Purchase #6 $98.61   7.406%   $105.9131   $105.91   $105.90   $105.90  
  Purchase #7 $236.97   6.441%   $252.2332   $252.23   $252.25   $252.20  
  7 purchase totals = $1,146.84       $1,241.3491   $1,241.35   $1,241.35   $1,241.30