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 $201.96   11.715%   $225.6196   $225.62   $225.60   $225.60  
  Purchase #2 $40.43   7.583%   $43.4958   $43.50   $43.50   $43.50  
  Purchase #3 $70.39   7.248%   $75.4919   $75.49   $75.50   $75.50  
  Purchase #4 $211.29   9.362%   $231.071   $231.07   $231.05   $231.10  
  Purchase #5 $23.85   13.745%   $27.1282   $27.13   $27.15   $27.10  
  Purchase #6 $52.26   7.344%   $56.098   $56.10   $56.10   $56.10  
  Purchase #7 $217.67   3.227%   $224.6942   $224.69   $224.70   $224.70  
  7 purchase totals = $817.85       $883.5987   $883.60   $883.60   $883.60