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 $106.86   5.784%   $113.0408   $113.04   $113.05   $113.00  
  Purchase #2 $213.95   13.136%   $242.0545   $242.05   $242.05   $242.10  
  Purchase #3 $43.68   10.264%   $48.1633   $48.16   $48.15   $48.20  
  Purchase #4 $33.85   3.243%   $34.9478   $34.95   $34.95   $34.90  
  Purchase #5 $166.62   6.318%   $177.1471   $177.15   $177.15   $177.10  
  Purchase #6 $26.35   5.722%   $27.8577   $27.86   $27.85   $27.90  
  Purchase #7 $120.58   13.473%   $136.8257   $136.83   $136.85   $136.80  
  7 purchase totals = $711.89       $780.0369   $780.04   $780.05   $780.00