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 $205.39   9.524%   $224.9513   $224.95   $224.95   $225.00  
  Purchase #2 $57.32   5.483%   $60.4629   $60.46   $60.45   $60.50  
  Purchase #3 $19.40   6.119%   $20.5871   $20.59   $20.60   $20.60  
  Purchase #4 $250.38   9.773%   $274.8496   $274.85   $274.85   $274.80  
  Purchase #5 $246.84   3.747%   $256.0891   $256.09   $256.10   $256.10  
  Purchase #6 $16.37   3.685%   $16.9732   $16.97   $16.95   $17.00  
  Purchase #7 $198.35   6.863%   $211.9628   $211.96   $211.95   $212.00  
  7 purchase totals = $994.05       $1,065.8760   $1,065.87   $1,065.85   $1,066.00