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 $114.81   4.771%   $120.2876   $120.29   $120.30   $120.30  
  Purchase #2 $236.70   12.418%   $266.0934   $266.09   $266.10   $266.10  
  Purchase #3 $62.33   11.204%   $69.3135   $69.31   $69.30   $69.30  
  Purchase #4 $63.54   6.277%   $67.5284   $67.53   $67.55   $67.50  
  Purchase #5 $198.69   3.317%   $205.2805   $205.28   $205.30   $205.30  
  Purchase #6 $248.53   12.273%   $279.0321   $279.03   $279.05   $279.00  
  Purchase #7 $46.97   11.833%   $52.528   $52.53   $52.55   $52.50  
  7 purchase totals = $971.57       $1,060.0635   $1,060.06   $1,060.15   $1,060.00