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 $96.41   6.403%   $102.5831   $102.58   $102.60   $102.60  
  Purchase #2 $229.84   4.250%   $239.6082   $239.61   $239.60   $239.60  
  Purchase #3 $245.92   9.399%   $269.034   $269.03   $269.05   $269.00  
  Purchase #4 $184.36   10.655%   $204.0036   $204.00   $204.00   $204.00  
  Purchase #5 $70.73   4.532%   $73.9355   $73.94   $73.95   $73.90  
  Purchase #6 $106.94   6.811%   $114.2237   $114.22   $114.20   $114.20  
  Purchase #7 $26.76   5.466%   $28.2227   $28.22   $28.20   $28.20  
  7 purchase totals = $960.96       $1,031.6108   $1,031.60   $1,031.60   $1,031.50