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 $135.25   8.755%   $147.0911   $147.09   $147.10   $147.10  
  Purchase #2 $139.85   10.669%   $154.7706   $154.77   $154.75   $154.80  
  Purchase #3 $90.43   12.111%   $101.382   $101.38   $101.40   $101.40  
  Purchase #4 $91.57   10.575%   $101.2535   $101.25   $101.25   $101.30  
  Purchase #5 $226.35   9.669%   $248.2358   $248.24   $248.25   $248.20  
  Purchase #6 $211.48   7.210%   $226.7277   $226.73   $226.75   $226.70  
  Purchase #7 $128.37   9.504%   $140.5703   $140.57   $140.55   $140.60  
  7 purchase totals = $1,023.30       $1,120.0310   $1,120.03   $1,120.05   $1,120.10