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 $216.30   4.643%   $226.3428   $226.34   $226.35   $226.30  
  Purchase #2 $211.55   11.443%   $235.7577   $235.76   $235.75   $235.80  
  Purchase #3 $148.97   9.504%   $163.1281   $163.13   $163.15   $163.10  
  Purchase #4 $53.69   4.765%   $56.2483   $56.25   $56.25   $56.20  
  Purchase #5 $113.81   9.102%   $124.169   $124.17   $124.15   $124.20  
  Purchase #6 $10.76   6.715%   $11.4825   $11.48   $11.50   $11.50  
  Purchase #7 $170.86   3.405%   $176.6778   $176.68   $176.70   $176.70  
  7 purchase totals = $925.94       $993.8062   $993.81   $993.85   $993.80