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 $59.52   13.529%   $67.5725   $67.57   $67.55   $67.60  
  Purchase #2 $174.62   9.325%   $190.9033   $190.90   $190.90   $190.90  
  Purchase #3 $155.81   8.238%   $168.6456   $168.65   $168.65   $168.60  
  Purchase #4 $144.62   11.375%   $161.0705   $161.07   $161.05   $161.10  
  Purchase #5 $14.40   8.859%   $15.6757   $15.68   $15.70   $15.70  
  Purchase #6 $77.59   6.860%   $82.9127   $82.91   $82.90   $82.90  
  Purchase #7 $214.68   9.580%   $235.2463   $235.25   $235.25   $235.20  
  7 purchase totals = $841.24       $922.0266   $922.03   $922.00   $922.00