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 $40.79   6.326%   $43.3704   $43.37   $43.35   $43.40  
  Purchase #2 $156.33   8.699%   $169.9291   $169.93   $169.95   $169.90  
  Purchase #3 $203.72   10.451%   $225.0108   $225.01   $225.00   $225.00  
  Purchase #4 $220.30   10.221%   $242.8169   $242.82   $242.80   $242.80  
  Purchase #5 $218.91   8.446%   $237.3991   $237.40   $237.40   $237.40  
  Purchase #6 $214.69   11.522%   $239.4266   $239.43   $239.45   $239.40  
  Purchase #7 $34.35   5.527%   $36.2485   $36.25   $36.25   $36.20  
  7 purchase totals = $1,089.09       $1,194.2014   $1,194.21   $1,194.20   $1,194.10