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 $168.54   6.108%   $178.8344   $178.83   $178.85   $178.80  
  Purchase #2 $18.57   7.415%   $19.947   $19.95   $19.95   $19.90  
  Purchase #3 $230.68   13.491%   $261.801   $261.80   $261.80   $261.80  
  Purchase #4 $46.65   11.493%   $52.0115   $52.01   $52.00   $52.00  
  Purchase #5 $89.33   10.832%   $99.0062   $99.01   $99.00   $99.00  
  Purchase #6 $65.51   10.233%   $72.2136   $72.21   $72.20   $72.20  
  Purchase #7 $243.93   10.593%   $269.7695   $269.77   $269.75   $269.80  
  7 purchase totals = $863.21       $953.5832   $953.58   $953.55   $953.50