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 $242.58   10.420%   $267.8568   $267.86   $267.85   $267.90  
  Purchase #2 $192.46   11.682%   $214.9432   $214.94   $214.95   $214.90  
  Purchase #3 $246.94   11.550%   $275.4616   $275.46   $275.45   $275.50  
  Purchase #4 $56.83   7.476%   $61.0786   $61.08   $61.10   $61.10  
  Purchase #5 $152.65   3.254%   $157.6172   $157.62   $157.60   $157.60  
  Purchase #6 $197.60   4.446%   $206.3853   $206.39   $206.40   $206.40  
  Purchase #7 $202.50   11.708%   $226.2087   $226.21   $226.20   $226.20  
  7 purchase totals = $1,291.56       $1,409.5514   $1,409.56   $1,409.55   $1,409.60