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 $182.80   11.247%   $203.3595   $203.36   $203.35   $203.40  
  Purchase #2 $30.81   4.624%   $32.2347   $32.23   $32.25   $32.20  
  Purchase #3 $214.54   13.811%   $244.1701   $244.17   $244.15   $244.20  
  Purchase #4 $107.80   7.633%   $116.0284   $116.03   $116.05   $116.00  
  Purchase #5 $248.37   13.380%   $281.6019   $281.60   $281.60   $281.60  
  Purchase #6 $97.43   9.770%   $106.9489   $106.95   $106.95   $106.90  
  Purchase #7 $198.27   6.574%   $211.3043   $211.30   $211.30   $211.30  
  7 purchase totals = $1,080.02       $1,195.6478   $1,195.64   $1,195.65   $1,195.60