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 $66.30   3.446%   $68.5847   $68.58   $68.60   $68.60  
  Purchase #2 $209.61   12.780%   $236.3982   $236.40   $236.40   $236.40  
  Purchase #3 $91.48   8.219%   $98.9987   $99.00   $99.00   $99.00  
  Purchase #4 $107.56   9.109%   $117.3576   $117.36   $117.35   $117.40  
  Purchase #5 $118.73   8.805%   $129.1842   $129.18   $129.20   $129.20  
  Purchase #6 $187.79   4.692%   $196.6011   $196.60   $196.60   $196.60  
  Purchase #7 $216.46   9.276%   $236.5388   $236.54   $236.55   $236.50  
  7 purchase totals = $997.93       $1,083.6633   $1,083.66   $1,083.70   $1,083.70