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 $58.39   10.821%   $64.7084   $64.71   $64.70   $64.70  
  Purchase #2 $146.64   6.410%   $156.0396   $156.04   $156.05   $156.00  
  Purchase #3 $101.94   3.742%   $105.7546   $105.75   $105.75   $105.80  
  Purchase #4 $222.77   13.393%   $252.6056   $252.61   $252.60   $252.60  
  Purchase #5 $206.90   4.688%   $216.5995   $216.60   $216.60   $216.60  
  Purchase #6 $247.64   7.427%   $266.0322   $266.03   $266.05   $266.00  
  Purchase #7 $53.67   13.107%   $60.7045   $60.70   $60.70   $60.70  
  7 purchase totals = $1,037.95       $1,122.4444   $1,122.44   $1,122.45   $1,122.40