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 $249.31   13.393%   $282.7001   $282.70   $282.70   $282.70  
  Purchase #2 $139.99   11.685%   $156.3478   $156.35   $156.35   $156.30  
  Purchase #3 $103.91   4.658%   $108.7501   $108.75   $108.75   $108.80  
  Purchase #4 $155.35   4.327%   $162.072   $162.07   $162.05   $162.10  
  Purchase #5 $8.68   10.199%   $9.5653   $9.57   $9.55   $9.60  
  Purchase #6 $217.78   11.373%   $242.5481   $242.55   $242.55   $242.50  
  Purchase #7 $61.28   6.238%   $65.1026   $65.10   $65.10   $65.10  
  7 purchase totals = $936.30       $1,027.0860   $1,027.09   $1,027.05   $1,027.10