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 $73.54   3.691%   $76.2544   $76.25   $76.25   $76.30  
  Purchase #2 $132.48   6.691%   $141.3442   $141.34   $141.35   $141.30  
  Purchase #3 $115.81   9.495%   $126.8062   $126.81   $126.80   $126.80  
  Purchase #4 $49.34   7.353%   $52.968   $52.97   $52.95   $53.00  
  Purchase #5 $63.86   9.312%   $69.8066   $69.81   $69.80   $69.80  
  Purchase #6 $141.47   4.440%   $147.7513   $147.75   $147.75   $147.80  
  Purchase #7 $197.65   3.106%   $203.789   $203.79   $203.80   $203.80  
  7 purchase totals = $774.15       $818.7197   $818.72   $818.70   $818.80