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 $68.38   13.717%   $77.7597   $77.76   $77.75   $77.80  
  Purchase #2 $208.43   8.442%   $226.0257   $226.03   $226.05   $226.00  
  Purchase #3 $218.96   9.637%   $240.0612   $240.06   $240.05   $240.10  
  Purchase #4 $61.61   3.429%   $63.7226   $63.72   $63.70   $63.70  
  Purchase #5 $200.60   13.239%   $227.1574   $227.16   $227.15   $227.20  
  Purchase #6 $109.38   9.419%   $119.6825   $119.68   $119.70   $119.70  
  Purchase #7 $181.37   3.242%   $187.25   $187.25   $187.25   $187.30  
  7 purchase totals = $1,048.73       $1,141.6591   $1,141.66   $1,141.65   $1,141.80