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 $235.55   11.523%   $262.6924   $262.69   $262.70   $262.70  
  Purchase #2 $175.94   12.232%   $197.461   $197.46   $197.45   $197.50  
  Purchase #3 $33.59   8.246%   $36.3598   $36.36   $36.35   $36.40  
  Purchase #4 $93.30   13.350%   $105.7556   $105.76   $105.75   $105.80  
  Purchase #5 $44.57   10.317%   $49.1683   $49.17   $49.15   $49.20  
  Purchase #6 $214.91   9.826%   $236.0271   $236.03   $236.05   $236.00  
  Purchase #7 $184.58   4.301%   $192.5188   $192.52   $192.50   $192.50  
  7 purchase totals = $982.44       $1,079.9830   $1,079.99   $1,079.95   $1,080.10