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 $61.61   13.172%   $69.7253   $69.73   $69.75   $69.70  
  Purchase #2 $86.42   8.134%   $93.4494   $93.45   $93.45   $93.40  
  Purchase #3 $214.92   11.863%   $240.416   $240.42   $240.40   $240.40  
  Purchase #4 $174.47   11.108%   $193.8501   $193.85   $193.85   $193.90  
  Purchase #5 $108.72   12.276%   $122.0665   $122.07   $122.05   $122.10  
  Purchase #6 $177.80   6.524%   $189.3997   $189.40   $189.40   $189.40  
  Purchase #7 $244.85   12.282%   $274.9225   $274.92   $274.90   $274.90  
  7 purchase totals = $1,068.79       $1,183.8295   $1,183.84   $1,183.80   $1,183.80