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 $208.25   13.825%   $237.0406   $237.04   $237.05   $237.00  
  Purchase #2 $67.41   10.253%   $74.3215   $74.32   $74.30   $74.30  
  Purchase #3 $223.90   13.789%   $254.7736   $254.77   $254.75   $254.80  
  Purchase #4 $182.26   4.352%   $190.192   $190.19   $190.20   $190.20  
  Purchase #5 $242.76   12.490%   $273.0807   $273.08   $273.10   $273.10  
  Purchase #6 $83.68   11.455%   $93.2655   $93.27   $93.25   $93.30  
  Purchase #7 $159.93   8.846%   $174.0774   $174.08   $174.10   $174.10  
  7 purchase totals = $1,168.19       $1,296.7513   $1,296.75   $1,296.75   $1,296.80