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 $126.82   13.173%   $143.526   $143.53   $143.55   $143.50  
  Purchase #2 $30.54   13.276%   $34.5945   $34.59   $34.60   $34.60  
  Purchase #3 $191.33   11.848%   $213.9988   $214.00   $214.00   $214.00  
  Purchase #4 $198.41   6.554%   $211.4138   $211.41   $211.40   $211.40  
  Purchase #5 $60.32   6.780%   $64.4097   $64.41   $64.40   $64.40  
  Purchase #6 $236.45   4.234%   $246.4613   $246.46   $246.45   $246.50  
  Purchase #7 $123.80   5.191%   $130.2265   $130.23   $130.25   $130.20  
  7 purchase totals = $967.67       $1,044.6306   $1,044.63   $1,044.65   $1,044.60