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 $88.47   9.348%   $96.7402   $96.74   $96.75   $96.70  
  Purchase #2 $143.92   13.626%   $163.5305   $163.53   $163.55   $163.50  
  Purchase #3 $96.55   8.702%   $104.9518   $104.95   $104.95   $105.00  
  Purchase #4 $249.53   13.605%   $283.4786   $283.48   $283.50   $283.50  
  Purchase #5 $75.42   12.476%   $84.8294   $84.83   $84.85   $84.80  
  Purchase #6 $10.63   3.806%   $11.0346   $11.03   $11.05   $11.00  
  Purchase #7 $165.46   7.206%   $177.383   $177.38   $177.40   $177.40  
  7 purchase totals = $829.98       $921.9481   $921.94   $922.05   $921.90