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 $30.49   5.869%   $32.2795   $32.28   $32.30   $32.30  
  Purchase #2 $139.86   5.180%   $147.1047   $147.10   $147.10   $147.10  
  Purchase #3 $116.50   4.623%   $121.8858   $121.89   $121.90   $121.90  
  Purchase #4 $204.94   4.502%   $214.1664   $214.17   $214.15   $214.20  
  Purchase #5 $51.99   11.202%   $57.8139   $57.81   $57.80   $57.80  
  Purchase #6 $174.27   10.507%   $192.5805   $192.58   $192.60   $192.60  
  Purchase #7 $167.55   11.379%   $186.6155   $186.62   $186.60   $186.60  
  7 purchase totals = $885.60       $952.4463   $952.45   $952.45   $952.50