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 $105.36   13.326%   $119.4003   $119.40   $119.40   $119.40  
  Purchase #2 $84.36   8.769%   $91.7575   $91.76   $91.75   $91.80  
  Purchase #3 $236.68   4.869%   $248.2039   $248.20   $248.20   $248.20  
  Purchase #4 $80.72   5.246%   $84.9546   $84.95   $84.95   $85.00  
  Purchase #5 $208.45   5.358%   $219.6188   $219.62   $219.60   $219.60  
  Purchase #6 $169.89   8.621%   $184.5362   $184.54   $184.55   $184.50  
  Purchase #7 $57.84   10.662%   $64.0069   $64.01   $64.00   $64.00  
  7 purchase totals = $943.30       $1,012.4782   $1,012.48   $1,012.45   $1,012.50