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 $126.33   12.705%   $142.3802   $142.38   $142.40   $142.40  
  Purchase #2 $186.50   11.554%   $208.0482   $208.05   $208.05   $208.00  
  Purchase #3 $178.46   12.570%   $200.8924   $200.89   $200.90   $200.90  
  Purchase #4 $228.85   6.233%   $243.1142   $243.11   $243.10   $243.10  
  Purchase #5 $184.31   11.861%   $206.171   $206.17   $206.15   $206.20  
  Purchase #6 $49.46   12.271%   $55.5292   $55.53   $55.55   $55.50  
  Purchase #7 $192.58   7.629%   $207.2719   $207.27   $207.25   $207.30  
  7 purchase totals = $1,146.49       $1,263.4071   $1,263.40   $1,263.40   $1,263.40