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 $56.77   7.772%   $61.1822   $61.18   $61.20   $61.20  
  Purchase #2 $184.98   5.174%   $194.5509   $194.55   $194.55   $194.60  
  Purchase #3 $182.65   5.493%   $192.683   $192.68   $192.70   $192.70  
  Purchase #4 $203.85   7.251%   $218.6312   $218.63   $218.65   $218.60  
  Purchase #5 $34.68   13.812%   $39.47   $39.47   $39.45   $39.50  
  Purchase #6 $22.83   8.191%   $24.7   $24.70   $24.70   $24.70  
  Purchase #7 $218.33   13.840%   $248.5469   $248.55   $248.55   $248.50  
  7 purchase totals = $904.09       $979.7642   $979.76   $979.80   $979.80