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 $169.76   8.473%   $184.1438   $184.14   $184.15   $184.10  
  Purchase #2 $58.41   4.813%   $61.2213   $61.22   $61.20   $61.20  
  Purchase #3 $58.78   8.140%   $63.5647   $63.56   $63.55   $63.60  
  Purchase #4 $165.63   4.598%   $173.2457   $173.25   $173.25   $173.20  
  Purchase #5 $110.68   9.681%   $121.3949   $121.39   $121.40   $121.40  
  Purchase #6 $61.45   3.292%   $63.4729   $63.47   $63.45   $63.50  
  Purchase #7 $120.54   8.271%   $130.5099   $130.51   $130.50   $130.50  
  7 purchase totals = $745.25       $797.5532   $797.54   $797.50   $797.50