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 $216.41   4.669%   $226.5142   $226.51   $226.50   $226.50  
  Purchase #2 $246.71   13.806%   $280.7708   $280.77   $280.75   $280.80  
  Purchase #3 $15.40   13.455%   $17.4721   $17.47   $17.45   $17.50  
  Purchase #4 $230.74   4.589%   $241.3287   $241.33   $241.35   $241.30  
  Purchase #5 $109.63   10.560%   $121.2069   $121.21   $121.20   $121.20  
  Purchase #6 $159.59   10.128%   $175.7533   $175.75   $175.75   $175.80  
  Purchase #7 $204.96   6.286%   $217.8438   $217.84   $217.85   $217.80  
  7 purchase totals = $1,183.44       $1,280.8898   $1,280.88   $1,280.85   $1,280.90