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 $222.91   13.727%   $253.5089   $253.51   $253.50   $253.50  
  Purchase #2 $188.27   10.547%   $208.1268   $208.13   $208.15   $208.10  
  Purchase #3 $232.27   4.227%   $242.0881   $242.09   $242.10   $242.10  
  Purchase #4 $249.90   6.311%   $265.6712   $265.67   $265.65   $265.70  
  Purchase #5 $109.26   3.429%   $113.0065   $113.01   $113.00   $113.00  
  Purchase #6 $211.92   11.644%   $236.596   $236.60   $236.60   $236.60  
  Purchase #7 $125.85   11.649%   $140.5103   $140.51   $140.50   $140.50  
  7 purchase totals = $1,340.38       $1,459.5078   $1,459.52   $1,459.50   $1,459.50