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 $130.61   12.567%   $147.0238   $147.02   $147.00   $147.00  
  Purchase #2 $38.27   13.789%   $43.5471   $43.55   $43.55   $43.50  
  Purchase #3 $124.95   4.705%   $130.8289   $130.83   $130.85   $130.80  
  Purchase #4 $229.62   4.868%   $240.7979   $240.80   $240.80   $240.80  
  Purchase #5 $236.88   13.226%   $268.2097   $268.21   $268.20   $268.20  
  Purchase #6 $227.39   12.838%   $256.5823   $256.58   $256.60   $256.60  
  Purchase #7 $92.80   5.605%   $98.0014   $98.00   $98.00   $98.00  
  7 purchase totals = $1,080.52       $1,184.9911   $1,184.99   $1,185.00   $1,184.90