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 $35.66   5.585%   $37.6516   $37.65   $37.65   $37.70  
  Purchase #2 $84.33   13.421%   $95.6479   $95.65   $95.65   $95.60  
  Purchase #3 $17.76   3.259%   $18.3388   $18.34   $18.35   $18.30  
  Purchase #4 $131.60   5.760%   $139.1802   $139.18   $139.20   $139.20  
  Purchase #5 $168.42   3.689%   $174.633   $174.63   $174.65   $174.60  
  Purchase #6 $49.44   5.577%   $52.1973   $52.20   $52.20   $52.20  
  Purchase #7 $153.25   3.596%   $158.7609   $158.76   $158.75   $158.80  
  7 purchase totals = $640.46       $676.4097   $676.41   $676.45   $676.40