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 $197.58   3.703%   $204.8964   $204.90   $204.90   $204.90  
  Purchase #2 $115.54   6.121%   $122.6122   $122.61   $122.60   $122.60  
  Purchase #3 $163.76   7.155%   $175.477   $175.48   $175.50   $175.50  
  Purchase #4 $12.99   8.825%   $14.1364   $14.14   $14.15   $14.10  
  Purchase #5 $200.25   11.727%   $223.7333   $223.73   $223.75   $223.70  
  Purchase #6 $61.81   3.246%   $63.8164   $63.82   $63.80   $63.80  
  Purchase #7 $211.26   3.314%   $218.2612   $218.26   $218.25   $218.30  
  7 purchase totals = $963.19       $1,022.9329   $1,022.94   $1,022.95   $1,022.90