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 $219.66   8.778%   $238.9418   $238.94   $238.95   $238.90  
  Purchase #2 $164.95   8.307%   $178.6524   $178.65   $178.65   $178.70  
  Purchase #3 $229.46   13.780%   $261.0796   $261.08   $261.10   $261.10  
  Purchase #4 $33.83   6.281%   $35.9549   $35.95   $35.95   $36.00  
  Purchase #5 $97.86   12.330%   $109.9261   $109.93   $109.95   $109.90  
  Purchase #6 $92.81   4.354%   $96.8509   $96.85   $96.85   $96.90  
  Purchase #7 $241.40   13.835%   $274.7977   $274.80   $274.80   $274.80  
  7 purchase totals = $1,079.97       $1,196.2034   $1,196.20   $1,196.25   $1,196.30