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 $108.86   7.828%   $117.3816   $117.38   $117.40   $117.40  
  Purchase #2 $198.87   4.527%   $207.8728   $207.87   $207.85   $207.90  
  Purchase #3 $21.59   4.862%   $22.6397   $22.64   $22.65   $22.60  
  Purchase #4 $68.32   8.352%   $74.0261   $74.03   $74.05   $74.00  
  Purchase #5 $109.46   4.281%   $114.146   $114.15   $114.15   $114.10  
  Purchase #6 $40.32   11.856%   $45.1003   $45.10   $45.10   $45.10  
  Purchase #7 $150.95   6.463%   $160.7059   $160.71   $160.70   $160.70  
  7 purchase totals = $698.37       $741.8724   $741.88   $741.90   $741.80