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 $220.62   10.477%   $243.7344   $243.73   $243.75   $243.70  
  Purchase #2 $175.37   5.503%   $185.0206   $185.02   $185.00   $185.00  
  Purchase #3 $184.48   4.397%   $192.5916   $192.59   $192.60   $192.60  
  Purchase #4 $106.32   10.774%   $117.7749   $117.77   $117.75   $117.80  
  Purchase #5 $175.74   10.721%   $194.5811   $194.58   $194.60   $194.60  
  Purchase #6 $84.96   9.586%   $93.1043   $93.10   $93.10   $93.10  
  Purchase #7 $38.61   4.367%   $40.2961   $40.30   $40.30   $40.30  
  7 purchase totals = $986.10       $1,067.1030   $1,067.09   $1,067.10   $1,067.10