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 $241.65   10.627%   $267.3301   $267.33   $267.35   $267.30  
  Purchase #2 $170.89   13.172%   $193.3996   $193.40   $193.40   $193.40  
  Purchase #3 $150.41   3.390%   $155.5089   $155.51   $155.50   $155.50  
  Purchase #4 $242.89   3.306%   $250.9199   $250.92   $250.90   $250.90  
  Purchase #5 $67.97   9.204%   $74.226   $74.23   $74.25   $74.20  
  Purchase #6 $7.50   8.181%   $8.1136   $8.11   $8.10   $8.10  
  Purchase #7 $171.67   9.808%   $188.5074   $188.51   $188.50   $188.50  
  7 purchase totals = $1,052.98       $1,138.0055   $1,138.01   $1,138.00   $1,137.90