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 $173.49   6.238%   $184.3123   $184.31   $184.30   $184.30  
  Purchase #2 $186.71   3.169%   $192.6268   $192.63   $192.65   $192.60  
  Purchase #3 $9.63   11.170%   $10.7057   $10.71   $10.70   $10.70  
  Purchase #4 $237.69   8.419%   $257.7011   $257.70   $257.70   $257.70  
  Purchase #5 $33.95   10.252%   $37.4306   $37.43   $37.45   $37.40  
  Purchase #6 $90.33   9.615%   $99.0152   $99.02   $99.00   $99.00  
  Purchase #7 $41.27   6.689%   $44.0306   $44.03   $44.05   $44.00  
  7 purchase totals = $773.07       $825.8223   $825.83   $825.85   $825.70