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 $93.41   10.867%   $103.5609   $103.56   $103.55   $103.60  
  Purchase #2 $161.64   9.840%   $177.5454   $177.55   $177.55   $177.50  
  Purchase #3 $218.52   4.637%   $228.6528   $228.65   $228.65   $228.70  
  Purchase #4 $168.81   4.350%   $176.1532   $176.15   $176.15   $176.20  
  Purchase #5 $77.49   11.328%   $86.2681   $86.27   $86.25   $86.30  
  Purchase #6 $183.30   5.692%   $193.7334   $193.73   $193.75   $193.70  
  Purchase #7 $200.99   12.840%   $226.7971   $226.80   $226.80   $226.80  
  7 purchase totals = $1,104.16       $1,192.7109   $1,192.71   $1,192.70   $1,192.80