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 $187.28   12.449%   $210.5945   $210.59   $210.60   $210.60  
  Purchase #2 $88.73   7.274%   $95.1842   $95.18   $95.20   $95.20  
  Purchase #3 $30.58   11.868%   $34.2092   $34.21   $34.20   $34.20  
  Purchase #4 $246.29   3.491%   $254.888   $254.89   $254.90   $254.90  
  Purchase #5 $227.59   10.115%   $250.6107   $250.61   $250.60   $250.60  
  Purchase #6 $107.74   9.139%   $117.5864   $117.59   $117.60   $117.60  
  Purchase #7 $84.55   10.554%   $93.4734   $93.47   $93.45   $93.50  
  7 purchase totals = $972.76       $1,056.5464   $1,056.54   $1,056.55   $1,056.60