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 $59.48   3.591%   $61.6159   $61.62   $61.60   $61.60  
  Purchase #2 $225.81   4.256%   $235.4205   $235.42   $235.40   $235.40  
  Purchase #3 $197.48   13.161%   $223.4703   $223.47   $223.45   $223.50  
  Purchase #4 $77.49   3.829%   $80.4571   $80.46   $80.45   $80.50  
  Purchase #5 $161.42   8.482%   $175.1116   $175.11   $175.10   $175.10  
  Purchase #6 $62.89   6.347%   $66.8816   $66.88   $66.90   $66.90  
  Purchase #7 $12.56   3.742%   $13.03   $13.03   $13.05   $13.00  
  7 purchase totals = $797.13       $855.9870   $855.99   $855.95   $856.00