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 $196.75   7.526%   $211.5574   $211.56   $211.55   $211.60  
  Purchase #2 $149.76   7.117%   $160.4184   $160.42   $160.40   $160.40  
  Purchase #3 $29.91   8.251%   $32.3779   $32.38   $32.40   $32.40  
  Purchase #4 $96.45   5.702%   $101.9496   $101.95   $101.95   $101.90  
  Purchase #5 $226.63   7.219%   $242.9904   $242.99   $243.00   $243.00  
  Purchase #6 $132.26   5.563%   $139.6176   $139.62   $139.60   $139.60  
  Purchase #7 $72.38   9.257%   $79.0802   $79.08   $79.10   $79.10  
  7 purchase totals = $904.14       $967.9915   $968.00   $968.00   $968.00