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 $92.77   5.812%   $98.1618   $98.16   $98.15   $98.20  
  Purchase #2 $121.53   10.780%   $134.6309   $134.63   $134.65   $134.60  
  Purchase #3 $236.68   4.388%   $247.0655   $247.07   $247.05   $247.10  
  Purchase #4 $54.94   9.698%   $60.2681   $60.27   $60.25   $60.30  
  Purchase #5 $208.81   9.154%   $227.9245   $227.92   $227.90   $227.90  
  Purchase #6 $66.83   11.627%   $74.6003   $74.60   $74.60   $74.60  
  Purchase #7 $197.52   5.297%   $207.9826   $207.98   $208.00   $208.00  
  7 purchase totals = $979.08       $1,050.6337   $1,050.63   $1,050.60   $1,050.70