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 $93.26   9.296%   $101.9294   $101.93   $101.95   $101.90  
  Purchase #2 $64.43   3.321%   $66.5697   $66.57   $66.55   $66.60  
  Purchase #3 $176.58   3.387%   $182.5608   $182.56   $182.55   $182.60  
  Purchase #4 $244.58   3.674%   $253.5659   $253.57   $253.55   $253.60  
  Purchase #5 $192.25   8.233%   $208.0779   $208.08   $208.10   $208.10  
  Purchase #6 $160.87   9.674%   $176.4326   $176.43   $176.45   $176.40  
  Purchase #7 $6.60   6.837%   $7.0512   $7.05   $7.05   $7.10  
  7 purchase totals = $938.57       $996.1875   $996.19   $996.20   $996.30