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 $176.77   10.156%   $194.7228   $194.72   $194.70   $194.70  
  Purchase #2 $121.94   6.240%   $129.5491   $129.55   $129.55   $129.50  
  Purchase #3 $225.40   10.418%   $248.8822   $248.88   $248.90   $248.90  
  Purchase #4 $124.98   3.270%   $129.0668   $129.07   $129.05   $129.10  
  Purchase #5 $242.85   9.321%   $265.486   $265.49   $265.50   $265.50  
  Purchase #6 $14.69   8.521%   $15.9417   $15.94   $15.95   $15.90  
  Purchase #7 $58.86   4.598%   $61.5664   $61.57   $61.55   $61.60  
  7 purchase totals = $965.49       $1,045.2150   $1,045.22   $1,045.20   $1,045.20