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 $86.91   5.843%   $91.9882   $91.99   $92.00   $92.00  
  Purchase #2 $246.32   9.205%   $268.9938   $268.99   $269.00   $269.00  
  Purchase #3 $243.61   13.547%   $276.6118   $276.61   $276.60   $276.60  
  Purchase #4 $86.95   5.588%   $91.8088   $91.81   $91.80   $91.80  
  Purchase #5 $36.45   10.867%   $40.411   $40.41   $40.40   $40.40  
  Purchase #6 $236.87   7.603%   $254.8792   $254.88   $254.90   $254.90  
  Purchase #7 $8.35   6.463%   $8.8897   $8.89   $8.90   $8.90  
  7 purchase totals = $945.46       $1,033.5825   $1,033.58   $1,033.60   $1,033.60