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 $244.54   4.135%   $254.6517   $254.65   $254.65   $254.70  
  Purchase #2 $12.57   4.280%   $13.108   $13.11   $13.10   $13.10  
  Purchase #3 $107.90   8.185%   $116.7316   $116.73   $116.75   $116.70  
  Purchase #4 $32.50   8.204%   $35.1663   $35.17   $35.15   $35.20  
  Purchase #5 $172.73   3.725%   $179.1642   $179.16   $179.15   $179.20  
  Purchase #6 $19.59   6.159%   $20.7965   $20.80   $20.80   $20.80  
  Purchase #7 $73.28   5.279%   $77.1485   $77.15   $77.15   $77.10  
  7 purchase totals = $663.11       $696.7668   $696.77   $696.75   $696.80