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 $61.53   3.266%   $63.5396   $63.54   $63.55   $63.50  
  Purchase #2 $188.58   9.537%   $206.5649   $206.56   $206.55   $206.60  
  Purchase #3 $105.81   8.788%   $115.1086   $115.11   $115.10   $115.10  
  Purchase #4 $145.72   8.455%   $158.0406   $158.04   $158.05   $158.00  
  Purchase #5 $17.38   8.372%   $18.8351   $18.84   $18.85   $18.80  
  Purchase #6 $34.28   6.143%   $36.3858   $36.39   $36.40   $36.40  
  Purchase #7 $192.52   4.333%   $200.8619   $200.86   $200.85   $200.90  
  7 purchase totals = $745.82       $799.3365   $799.34   $799.35   $799.30