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 $70.85   4.113%   $73.7641   $73.76   $73.75   $73.80  
  Purchase #2 $229.95   3.717%   $238.4972   $238.50   $238.50   $238.50  
  Purchase #3 $62.35   7.462%   $67.0026   $67.00   $67.00   $67.00  
  Purchase #4 $209.62   8.342%   $227.1065   $227.11   $227.10   $227.10  
  Purchase #5 $56.55   7.569%   $60.8303   $60.83   $60.85   $60.80  
  Purchase #6 $243.93   6.449%   $259.661   $259.66   $259.65   $259.70  
  Purchase #7 $45.81   3.257%   $47.302   $47.30   $47.30   $47.30  
  7 purchase totals = $919.06       $974.1637   $974.16   $974.15   $974.20