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 $83.91   11.154%   $93.2693   $93.27   $93.25   $93.30  
  Purchase #2 $169.98   13.196%   $192.4106   $192.41   $192.40   $192.40  
  Purchase #3 $136.76   11.635%   $152.672   $152.67   $152.65   $152.70  
  Purchase #4 $63.66   9.589%   $69.7644   $69.76   $69.75   $69.80  
  Purchase #5 $222.52   6.807%   $237.6669   $237.67   $237.65   $237.70  
  Purchase #6 $188.97   13.357%   $214.2107   $214.21   $214.20   $214.20  
  Purchase #7 $86.83   3.558%   $89.9194   $89.92   $89.90   $89.90  
  7 purchase totals = $952.63       $1,049.9133   $1,049.91   $1,049.80   $1,050.00