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 $53.85   4.670%   $56.3648   $56.36   $56.35   $56.40  
  Purchase #2 $193.52   8.851%   $210.6485   $210.65   $210.65   $210.60  
  Purchase #3 $106.95   4.650%   $111.9232   $111.92   $111.90   $111.90  
  Purchase #4 $157.61   11.797%   $176.2033   $176.20   $176.20   $176.20  
  Purchase #5 $62.29   3.849%   $64.6875   $64.69   $64.70   $64.70  
  Purchase #6 $212.98   12.757%   $240.1499   $240.15   $240.15   $240.10  
  Purchase #7 $53.76   12.857%   $60.6719   $60.67   $60.65   $60.70  
  7 purchase totals = $840.96       $920.6491   $920.64   $920.60   $920.60