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 $220.56   11.377%   $245.6531   $245.65   $245.65   $245.70  
  Purchase #2 $126.91   4.807%   $133.0106   $133.01   $133.00   $133.00  
  Purchase #3 $194.61   5.418%   $205.154   $205.15   $205.15   $205.20  
  Purchase #4 $19.97   11.458%   $22.2582   $22.26   $22.25   $22.30  
  Purchase #5 $76.55   5.528%   $80.7817   $80.78   $80.80   $80.80  
  Purchase #6 $130.95   5.249%   $137.8236   $137.82   $137.80   $137.80  
  Purchase #7 $214.77   12.199%   $240.9698   $240.97   $240.95   $241.00  
  7 purchase totals = $984.32       $1,065.6510   $1,065.64   $1,065.60   $1,065.80