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 $165.84   6.651%   $176.87   $176.87   $176.85   $176.90  
  Purchase #2 $42.37   12.528%   $47.6781   $47.68   $47.70   $47.70  
  Purchase #3 $208.81   6.791%   $222.9903   $222.99   $223.00   $223.00  
  Purchase #4 $233.82   12.826%   $263.8098   $263.81   $263.80   $263.80  
  Purchase #5 $147.32   4.219%   $153.5354   $153.54   $153.55   $153.50  
  Purchase #6 $237.66   13.808%   $270.4761   $270.48   $270.50   $270.50  
  Purchase #7 $206.32   4.603%   $215.8169   $215.82   $215.80   $215.80  
  7 purchase totals = $1,242.14       $1,351.1766   $1,351.19   $1,351.20   $1,351.20