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 $42.66   3.872%   $44.3118   $44.31   $44.30   $44.30  
  Purchase #2 $150.49   8.535%   $163.3343   $163.33   $163.35   $163.30  
  Purchase #3 $164.30   11.238%   $182.764   $182.76   $182.75   $182.80  
  Purchase #4 $160.91   3.758%   $166.957   $166.96   $166.95   $167.00  
  Purchase #5 $171.30   10.769%   $189.7473   $189.75   $189.75   $189.70  
  Purchase #6 $90.56   11.186%   $100.69   $100.69   $100.70   $100.70  
  Purchase #7 $65.70   9.721%   $72.0867   $72.09   $72.10   $72.10  
  7 purchase totals = $845.92       $919.8911   $919.89   $919.90   $919.90