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 $108.34   13.845%   $123.3397   $123.34   $123.35   $123.30  
  Purchase #2 $226.74   10.376%   $250.2665   $250.27   $250.25   $250.30  
  Purchase #3 $193.41   6.642%   $206.2563   $206.26   $206.25   $206.30  
  Purchase #4 $42.45   11.257%   $47.2286   $47.23   $47.25   $47.20  
  Purchase #5 $99.78   4.870%   $104.6393   $104.64   $104.65   $104.60  
  Purchase #6 $168.62   3.829%   $175.0765   $175.08   $175.10   $175.10  
  Purchase #7 $106.78   8.423%   $115.7741   $115.77   $115.75   $115.80  
  7 purchase totals = $946.12       $1,022.5810   $1,022.59   $1,022.60   $1,022.60