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 $236.70   13.841%   $269.4616   $269.46   $269.45   $269.50  
  Purchase #2 $166.53   11.705%   $186.0223   $186.02   $186.00   $186.00  
  Purchase #3 $148.50   4.337%   $154.9404   $154.94   $154.95   $154.90  
  Purchase #4 $79.64   12.470%   $89.5711   $89.57   $89.55   $89.60  
  Purchase #5 $47.87   3.621%   $49.6034   $49.60   $49.60   $49.60  
  Purchase #6 $162.33   9.292%   $177.4137   $177.41   $177.40   $177.40  
  Purchase #7 $224.33   3.484%   $232.1457   $232.15   $232.15   $232.10  
  7 purchase totals = $1,065.90       $1,159.1582   $1,159.15   $1,159.10   $1,159.10