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 $63.62   5.785%   $67.3004   $67.30   $67.30   $67.30  
  Purchase #2 $239.91   6.529%   $255.5737   $255.57   $255.55   $255.60  
  Purchase #3 $45.77   6.262%   $48.6361   $48.64   $48.65   $48.60  
  Purchase #4 $206.94   7.406%   $222.266   $222.27   $222.25   $222.30  
  Purchase #5 $14.64   11.588%   $16.3365   $16.34   $16.35   $16.30  
  Purchase #6 $171.39   3.820%   $177.9371   $177.94   $177.95   $177.90  
  Purchase #7 $248.72   8.614%   $270.1447   $270.14   $270.15   $270.10  
  7 purchase totals = $990.99       $1,058.1945   $1,058.20   $1,058.20   $1,058.10