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 $238.26   3.501%   $246.6015   $246.60   $246.60   $246.60  
  Purchase #2 $131.80   9.372%   $144.1523   $144.15   $144.15   $144.20  
  Purchase #3 $55.90   13.207%   $63.2827   $63.28   $63.30   $63.30  
  Purchase #4 $141.40   4.226%   $147.3756   $147.38   $147.40   $147.40  
  Purchase #5 $80.96   8.847%   $88.1225   $88.12   $88.10   $88.10  
  Purchase #6 $105.71   8.465%   $114.6584   $114.66   $114.65   $114.70  
  Purchase #7 $193.45   6.586%   $206.1906   $206.19   $206.20   $206.20  
  7 purchase totals = $947.48       $1,010.3836   $1,010.38   $1,010.40   $1,010.50