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 $51.74   9.389%   $56.5979   $56.60   $56.60   $56.60  
  Purchase #2 $226.49   5.846%   $239.7306   $239.73   $239.75   $239.70  
  Purchase #3 $56.71   7.236%   $60.8135   $60.81   $60.80   $60.80  
  Purchase #4 $215.47   5.152%   $226.571   $226.57   $226.55   $226.60  
  Purchase #5 $184.95   9.789%   $203.0548   $203.05   $203.05   $203.10  
  Purchase #6 $113.96   12.601%   $128.3201   $128.32   $128.30   $128.30  
  Purchase #7 $134.98   6.726%   $144.0588   $144.06   $144.05   $144.10  
  7 purchase totals = $984.30       $1,059.1467   $1,059.14   $1,059.10   $1,059.20