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 $193.57   5.647%   $204.5009   $204.50   $204.50   $204.50  
  Purchase #2 $112.40   4.686%   $117.6671   $117.67   $117.65   $117.70  
  Purchase #3 $14.69   6.131%   $15.5906   $15.59   $15.60   $15.60  
  Purchase #4 $182.82   12.515%   $205.6999   $205.70   $205.70   $205.70  
  Purchase #5 $80.85   3.389%   $83.59   $83.59   $83.60   $83.60  
  Purchase #6 $35.90   8.721%   $39.0308   $39.03   $39.05   $39.00  
  Purchase #7 $72.57   9.752%   $79.647   $79.65   $79.65   $79.60  
  7 purchase totals = $692.80       $745.7263   $745.73   $745.75   $745.70