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 $248.43   13.738%   $282.5593   $282.56   $282.55   $282.60  
  Purchase #2 $208.52   13.540%   $236.7536   $236.75   $236.75   $236.80  
  Purchase #3 $15.88   11.418%   $17.6932   $17.69   $17.70   $17.70  
  Purchase #4 $36.57   5.344%   $38.5243   $38.52   $38.50   $38.50  
  Purchase #5 $213.97   8.696%   $232.5768   $232.58   $232.60   $232.60  
  Purchase #6 $154.60   11.313%   $172.0899   $172.09   $172.10   $172.10  
  Purchase #7 $186.47   8.652%   $202.6034   $202.60   $202.60   $202.60  
  7 purchase totals = $1,064.44       $1,182.8005   $1,182.79   $1,182.80   $1,182.90