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 $250.77   4.818%   $262.8521   $262.85   $262.85   $262.90  
  Purchase #2 $131.98   7.313%   $141.6317   $141.63   $141.65   $141.60  
  Purchase #3 $143.86   5.846%   $152.2701   $152.27   $152.25   $152.30  
  Purchase #4 $76.88   11.827%   $85.9726   $85.97   $85.95   $86.00  
  Purchase #5 $228.70   4.582%   $239.179   $239.18   $239.20   $239.20  
  Purchase #6 $241.71   13.174%   $273.5529   $273.55   $273.55   $273.60  
  Purchase #7 $192.59   6.351%   $204.8214   $204.82   $204.80   $204.80  
  7 purchase totals = $1,266.49       $1,360.2798   $1,360.27   $1,360.25   $1,360.40