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 $91.40   5.229%   $96.1793   $96.18   $96.20   $96.20  
  Purchase #2 $112.62   8.577%   $122.2794   $122.28   $122.30   $122.30  
  Purchase #3 $36.32   8.203%   $39.2993   $39.30   $39.30   $39.30  
  Purchase #4 $241.49   13.715%   $274.6104   $274.61   $274.60   $274.60  
  Purchase #5 $86.59   11.716%   $96.7349   $96.73   $96.75   $96.70  
  Purchase #6 $11.48   7.702%   $12.3642   $12.36   $12.35   $12.40  
  Purchase #7 $140.48   11.241%   $156.2714   $156.27   $156.25   $156.30  
  7 purchase totals = $720.38       $797.7389   $797.73   $797.75   $797.80