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 $120.41   8.126%   $130.1945   $130.19   $130.20   $130.20  
  Purchase #2 $195.67   4.244%   $203.9742   $203.97   $203.95   $204.00  
  Purchase #3 $248.58   8.521%   $269.7615   $269.76   $269.75   $269.80  
  Purchase #4 $120.77   4.421%   $126.1092   $126.11   $126.10   $126.10  
  Purchase #5 $64.95   13.131%   $73.4786   $73.48   $73.50   $73.50  
  Purchase #6 $195.42   6.432%   $207.9894   $207.99   $208.00   $208.00  
  Purchase #7 $60.25   4.562%   $62.9986   $63.00   $63.00   $63.00  
  7 purchase totals = $1,006.05       $1,074.5060   $1,074.50   $1,074.50   $1,074.60