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 $240.56   9.471%   $263.3434   $263.34   $263.35   $263.30  
  Purchase #2 $55.95   4.830%   $58.6524   $58.65   $58.65   $58.70  
  Purchase #3 $102.56   11.263%   $114.1113   $114.11   $114.10   $114.10  
  Purchase #4 $222.54   13.353%   $252.2558   $252.26   $252.25   $252.30  
  Purchase #5 $214.43   8.831%   $233.3663   $233.37   $233.35   $233.40  
  Purchase #6 $54.95   10.474%   $60.7055   $60.71   $60.70   $60.70  
  Purchase #7 $171.58   8.313%   $185.8434   $185.84   $185.85   $185.80  
  7 purchase totals = $1,062.57       $1,168.2781   $1,168.28   $1,168.25   $1,168.30