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 $108.68   12.489%   $122.253   $122.25   $122.25   $122.30  
  Purchase #2 $189.57   13.154%   $214.506   $214.51   $214.50   $214.50  
  Purchase #3 $227.84   13.173%   $257.8534   $257.85   $257.85   $257.90  
  Purchase #4 $171.32   4.837%   $179.6067   $179.61   $179.60   $179.60  
  Purchase #5 $247.89   7.158%   $265.634   $265.63   $265.65   $265.60  
  Purchase #6 $72.99   8.134%   $78.927   $78.93   $78.95   $78.90  
  Purchase #7 $41.39   7.710%   $44.5812   $44.58   $44.60   $44.60  
  7 purchase totals = $1,059.68       $1,163.3613   $1,163.36   $1,163.40   $1,163.40