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 $185.88   10.835%   $206.0201   $206.02   $206.00   $206.00  
  Purchase #2 $32.59   9.867%   $35.8057   $35.81   $35.80   $35.80  
  Purchase #3 $19.84   8.864%   $21.5986   $21.60   $21.60   $21.60  
  Purchase #4 $211.47   12.294%   $237.4681   $237.47   $237.45   $237.50  
  Purchase #5 $221.53   5.467%   $233.641   $233.64   $233.65   $233.60  
  Purchase #6 $40.78   9.153%   $44.5126   $44.51   $44.50   $44.50  
  Purchase #7 $71.76   10.125%   $79.0257   $79.03   $79.05   $79.00  
  7 purchase totals = $783.85       $858.0718   $858.08   $858.05   $858.00