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 $61.40   11.235%   $68.2983   $68.30   $68.30   $68.30  
  Purchase #2 $193.48   4.192%   $201.5907   $201.59   $201.60   $201.60  
  Purchase #3 $124.27   13.626%   $141.203   $141.20   $141.20   $141.20  
  Purchase #4 $91.58   10.329%   $101.0393   $101.04   $101.05   $101.00  
  Purchase #5 $111.32   4.705%   $116.5576   $116.56   $116.55   $116.60  
  Purchase #6 $240.67   3.173%   $248.3065   $248.31   $248.30   $248.30  
  Purchase #7 $145.92   11.155%   $162.1974   $162.20   $162.20   $162.20  
  7 purchase totals = $968.64       $1,039.1928   $1,039.20   $1,039.20   $1,039.20