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 $52.82   8.562%   $57.3424   $57.34   $57.35   $57.30  
  Purchase #2 $223.25   9.566%   $244.6061   $244.61   $244.60   $244.60  
  Purchase #3 $55.41   3.807%   $57.5195   $57.52   $57.50   $57.50  
  Purchase #4 $248.71   4.535%   $259.989   $259.99   $260.00   $260.00  
  Purchase #5 $183.95   3.800%   $190.9401   $190.94   $190.95   $190.90  
  Purchase #6 $113.41   12.371%   $127.44   $127.44   $127.45   $127.40  
  Purchase #7 $16.48   3.193%   $17.0062   $17.01   $17.00   $17.00  
  7 purchase totals = $894.03       $954.8433   $954.85   $954.85   $954.70