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 $250.56   9.258%   $273.7568   $273.76   $273.75   $273.80  
  Purchase #2 $241.69   4.492%   $252.5467   $252.55   $252.55   $252.50  
  Purchase #3 $205.98   13.273%   $233.3197   $233.32   $233.30   $233.30  
  Purchase #4 $207.51   11.790%   $231.9754   $231.98   $232.00   $232.00  
  Purchase #5 $200.63   12.123%   $224.9524   $224.95   $224.95   $225.00  
  Purchase #6 $76.96   4.832%   $80.6787   $80.68   $80.70   $80.70  
  Purchase #7 $161.45   5.442%   $170.2361   $170.24   $170.25   $170.20  
  7 purchase totals = $1,344.78       $1,467.4658   $1,467.48   $1,467.50   $1,467.50