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 $192.44   12.188%   $215.8946   $215.89   $215.90   $215.90  
  Purchase #2 $242.61   8.774%   $263.8966   $263.90   $263.90   $263.90  
  Purchase #3 $221.29   11.727%   $247.2407   $247.24   $247.25   $247.20  
  Purchase #4 $86.76   10.629%   $95.9817   $95.98   $96.00   $96.00  
  Purchase #5 $56.75   12.192%   $63.669   $63.67   $63.65   $63.70  
  Purchase #6 $58.60   10.629%   $64.8286   $64.83   $64.85   $64.80  
  Purchase #7 $57.70   7.257%   $61.8873   $61.89   $61.90   $61.90  
  7 purchase totals = $916.15       $1,013.3985   $1,013.40   $1,013.45   $1,013.40