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 $124.82   5.564%   $131.765   $131.77   $131.75   $131.80  
  Purchase #2 $242.85   9.189%   $265.1655   $265.17   $265.15   $265.20  
  Purchase #3 $151.35   7.245%   $162.3153   $162.32   $162.30   $162.30  
  Purchase #4 $166.59   4.451%   $174.0049   $174.00   $174.00   $174.00  
  Purchase #5 $126.45   3.113%   $130.3864   $130.39   $130.40   $130.40  
  Purchase #6 $238.66   5.571%   $251.9557   $251.96   $251.95   $252.00  
  Purchase #7 $173.66   6.799%   $185.4671   $185.47   $185.45   $185.50  
  7 purchase totals = $1,224.38       $1,301.0599   $1,301.08   $1,301.00   $1,301.20