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 $57.99   6.379%   $61.6892   $61.69   $61.70   $61.70  
  Purchase #2 $182.82   9.658%   $200.4768   $200.48   $200.50   $200.50  
  Purchase #3 $27.73   6.216%   $29.4537   $29.45   $29.45   $29.50  
  Purchase #4 $60.96   9.419%   $66.7018   $66.70   $66.70   $66.70  
  Purchase #5 $50.81   13.592%   $57.7161   $57.72   $57.70   $57.70  
  Purchase #6 $163.56   13.241%   $185.217   $185.22   $185.20   $185.20  
  Purchase #7 $148.42   6.328%   $157.812   $157.81   $157.80   $157.80  
  7 purchase totals = $692.29       $759.0666   $759.07   $759.05   $759.10