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 $109.56   13.750%   $124.6245   $124.62   $124.60   $124.60  
  Purchase #2 $121.57   12.324%   $136.5523   $136.55   $136.55   $136.60  
  Purchase #3 $186.79   11.835%   $208.8966   $208.90   $208.90   $208.90  
  Purchase #4 $58.57   7.480%   $62.951   $62.95   $62.95   $63.00  
  Purchase #5 $73.69   4.846%   $77.261   $77.26   $77.25   $77.30  
  Purchase #6 $211.69   7.505%   $227.5773   $227.58   $227.60   $227.60  
  Purchase #7 $197.52   13.416%   $224.0193   $224.02   $224.00   $224.00  
  7 purchase totals = $959.39       $1,061.8820   $1,061.88   $1,061.85   $1,062.00