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 $57.31   4.571%   $59.9296   $59.93   $59.95   $59.90  
  Purchase #2 $233.34   7.305%   $250.3855   $250.39   $250.40   $250.40  
  Purchase #3 $241.45   6.724%   $257.6851   $257.69   $257.70   $257.70  
  Purchase #4 $223.39   9.836%   $245.3626   $245.36   $245.35   $245.40  
  Purchase #5 $87.38   12.207%   $98.0465   $98.05   $98.05   $98.00  
  Purchase #6 $213.46   3.232%   $220.359   $220.36   $220.35   $220.40  
  Purchase #7 $217.50   12.874%   $245.501   $245.50   $245.50   $245.50  
  7 purchase totals = $1,273.83       $1,377.2693   $1,377.28   $1,377.30   $1,377.30