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 $197.51   3.768%   $204.9522   $204.95   $204.95   $205.00  
  Purchase #2 $8.75   10.665%   $9.6832   $9.68   $9.70   $9.70  
  Purchase #3 $176.83   5.525%   $186.5999   $186.60   $186.60   $186.60  
  Purchase #4 $32.28   9.780%   $35.437   $35.44   $35.45   $35.40  
  Purchase #5 $102.73   13.631%   $116.7331   $116.73   $116.75   $116.70  
  Purchase #6 $233.95   5.240%   $246.209   $246.21   $246.20   $246.20  
  Purchase #7 $20.64   10.787%   $22.8664   $22.87   $22.85   $22.90  
  7 purchase totals = $772.69       $822.4808   $822.48   $822.50   $822.50