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 $133.84   10.782%   $148.2706   $148.27   $148.25   $148.30  
  Purchase #2 $91.29   11.369%   $101.6688   $101.67   $101.65   $101.70  
  Purchase #3 $37.76   6.678%   $40.2816   $40.28   $40.30   $40.30  
  Purchase #4 $172.27   9.563%   $188.7442   $188.74   $188.75   $188.70  
  Purchase #5 $126.66   5.795%   $133.9999   $134.00   $134.00   $134.00  
  Purchase #6 $218.71   9.522%   $239.5356   $239.54   $239.55   $239.50  
  Purchase #7 $184.94   3.806%   $191.9788   $191.98   $192.00   $192.00  
  7 purchase totals = $965.47       $1,044.4795   $1,044.48   $1,044.50   $1,044.50