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 $125.57   11.529%   $140.047   $140.05   $140.05   $140.00  
  Purchase #2 $41.32   13.742%   $46.9982   $47.00   $47.00   $47.00  
  Purchase #3 $244.85   11.232%   $272.3516   $272.35   $272.35   $272.40  
  Purchase #4 $56.69   12.543%   $63.8006   $63.80   $63.80   $63.80  
  Purchase #5 $83.62   4.129%   $87.0727   $87.07   $87.05   $87.10  
  Purchase #6 $241.80   10.175%   $266.4032   $266.40   $266.40   $266.40  
  Purchase #7 $147.55   3.409%   $152.58   $152.58   $152.60   $152.60  
  7 purchase totals = $941.40       $1,029.2533   $1,029.25   $1,029.25   $1,029.30