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 $195.88   6.559%   $208.7278   $208.73   $208.75   $208.70  
  Purchase #2 $242.45   9.155%   $264.6463   $264.65   $264.65   $264.60  
  Purchase #3 $214.75   9.748%   $235.6838   $235.68   $235.70   $235.70  
  Purchase #4 $166.41   6.220%   $176.7607   $176.76   $176.75   $176.80  
  Purchase #5 $87.75   8.637%   $95.329   $95.33   $95.35   $95.30  
  Purchase #6 $239.94   12.251%   $269.335   $269.34   $269.35   $269.30  
  Purchase #7 $241.78   6.580%   $257.6891   $257.69   $257.70   $257.70  
  7 purchase totals = $1,388.96       $1,508.1717   $1,508.18   $1,508.25   $1,508.10