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 $235.95   4.415%   $246.3672   $246.37   $246.35   $246.40  
  Purchase #2 $32.99   8.287%   $35.7239   $35.72   $35.70   $35.70  
  Purchase #3 $184.54   10.494%   $203.9056   $203.91   $203.90   $203.90  
  Purchase #4 $242.44   4.849%   $254.1959   $254.20   $254.20   $254.20  
  Purchase #5 $88.54   11.328%   $98.5698   $98.57   $98.55   $98.60  
  Purchase #6 $224.26   5.781%   $237.2245   $237.22   $237.20   $237.20  
  Purchase #7 $150.58   3.649%   $156.0747   $156.07   $156.05   $156.10  
  7 purchase totals = $1,159.30       $1,232.0616   $1,232.06   $1,231.95   $1,232.10