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 $50.91   13.212%   $57.6362   $57.64   $57.65   $57.60  
  Purchase #2 $117.81   9.816%   $129.3742   $129.37   $129.35   $129.40  
  Purchase #3 $59.53   13.687%   $67.6779   $67.68   $67.70   $67.70  
  Purchase #4 $95.71   6.767%   $102.1867   $102.19   $102.20   $102.20  
  Purchase #5 $204.32   7.382%   $219.4029   $219.40   $219.40   $219.40  
  Purchase #6 $6.51   4.659%   $6.8133   $6.81   $6.80   $6.80  
  Purchase #7 $197.64   3.260%   $204.0831   $204.08   $204.10   $204.10  
  7 purchase totals = $732.43       $787.1743   $787.17   $787.20   $787.20