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 $53.61   13.768%   $60.991   $60.99   $61.00   $61.00  
  Purchase #2 $154.95   11.169%   $172.2564   $172.26   $172.25   $172.30  
  Purchase #3 $232.40   10.591%   $257.0135   $257.01   $257.00   $257.00  
  Purchase #4 $218.30   9.626%   $239.3136   $239.31   $239.30   $239.30  
  Purchase #5 $233.90   6.261%   $248.5445   $248.54   $248.55   $248.50  
  Purchase #6 $24.75   3.240%   $25.5519   $25.55   $25.55   $25.60  
  Purchase #7 $8.26   8.376%   $8.9519   $8.95   $8.95   $9.00  
  7 purchase totals = $926.17       $1,012.6228   $1,012.61   $1,012.60   $1,012.70