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 $51.94   7.229%   $55.6947   $55.69   $55.70   $55.70  
  Purchase #2 $170.73   13.576%   $193.9083   $193.91   $193.90   $193.90  
  Purchase #3 $81.67   4.209%   $85.1075   $85.11   $85.10   $85.10  
  Purchase #4 $69.35   11.182%   $77.1047   $77.10   $77.10   $77.10  
  Purchase #5 $91.31   4.186%   $95.1322   $95.13   $95.15   $95.10  
  Purchase #6 $236.76   9.776%   $259.9057   $259.91   $259.90   $259.90  
  Purchase #7 $243.66   3.733%   $252.7558   $252.76   $252.75   $252.80  
  7 purchase totals = $945.42       $1,019.6089   $1,019.61   $1,019.60   $1,019.60