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 $123.96   13.447%   $140.6289   $140.63   $140.65   $140.60  
  Purchase #2 $225.51   4.243%   $235.0784   $235.08   $235.10   $235.10  
  Purchase #3 $160.82   11.118%   $178.7   $178.70   $178.70   $178.70  
  Purchase #4 $152.56   3.499%   $157.8981   $157.90   $157.90   $157.90  
  Purchase #5 $165.55   7.269%   $177.5838   $177.58   $177.60   $177.60  
  Purchase #6 $163.28   13.369%   $185.1089   $185.11   $185.10   $185.10  
  Purchase #7 $198.85   11.446%   $221.6104   $221.61   $221.60   $221.60  
  7 purchase totals = $1,190.53       $1,296.6085   $1,296.61   $1,296.65   $1,296.60