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 $231.59   12.495%   $260.5272   $260.53   $260.55   $260.50  
  Purchase #2 $171.81   11.477%   $191.5286   $191.53   $191.55   $191.50  
  Purchase #3 $63.60   7.851%   $68.5932   $68.59   $68.60   $68.60  
  Purchase #4 $134.88   6.533%   $143.6917   $143.69   $143.70   $143.70  
  Purchase #5 $218.36   11.747%   $244.0107   $244.01   $244.00   $244.00  
  Purchase #6 $110.36   8.591%   $119.841   $119.84   $119.85   $119.80  
  Purchase #7 $85.33   12.590%   $96.073   $96.07   $96.05   $96.10  
  7 purchase totals = $1,015.93       $1,124.2654   $1,124.26   $1,124.30   $1,124.20