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 $79.88   8.544%   $86.7049   $86.70   $86.70   $86.70  
  Purchase #2 $85.63   6.546%   $91.2353   $91.24   $91.25   $91.20  
  Purchase #3 $141.83   12.443%   $159.4779   $159.48   $159.50   $159.50  
  Purchase #4 $167.82   10.228%   $184.9846   $184.98   $185.00   $185.00  
  Purchase #5 $102.51   9.866%   $112.6236   $112.62   $112.60   $112.60  
  Purchase #6 $228.64   4.815%   $239.649   $239.65   $239.65   $239.60  
  Purchase #7 $117.62   7.645%   $126.612   $126.61   $126.60   $126.60  
  7 purchase totals = $923.93       $1,001.2873   $1,001.28   $1,001.30   $1,001.20