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 $239.52   8.396%   $259.6301   $259.63   $259.65   $259.60  
  Purchase #2 $103.35   11.371%   $115.1019   $115.10   $115.10   $115.10  
  Purchase #3 $34.77   5.493%   $36.6799   $36.68   $36.70   $36.70  
  Purchase #4 $235.61   6.771%   $251.5632   $251.56   $251.55   $251.60  
  Purchase #5 $38.63   13.854%   $43.9818   $43.98   $44.00   $44.00  
  Purchase #6 $109.69   9.719%   $120.3508   $120.35   $120.35   $120.40  
  Purchase #7 $125.58   5.129%   $132.021   $132.02   $132.00   $132.00  
  7 purchase totals = $887.15       $959.3287   $959.32   $959.35   $959.40