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 $171.50   13.482%   $194.6216   $194.62   $194.60   $194.60  
  Purchase #2 $249.85   7.660%   $268.9885   $268.99   $269.00   $269.00  
  Purchase #3 $53.38   7.239%   $57.2442   $57.24   $57.25   $57.20  
  Purchase #4 $116.44   7.453%   $125.1183   $125.12   $125.10   $125.10  
  Purchase #5 $145.51   3.171%   $150.1241   $150.12   $150.10   $150.10  
  Purchase #6 $108.27   5.355%   $114.0679   $114.07   $114.05   $114.10  
  Purchase #7 $137.44   8.403%   $148.9891   $148.99   $149.00   $149.00  
  7 purchase totals = $982.39       $1,059.1537   $1,059.15   $1,059.10   $1,059.10