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 $243.93   5.603%   $257.5974   $257.60   $257.60   $257.60  
  Purchase #2 $58.42   4.543%   $61.074   $61.07   $61.05   $61.10  
  Purchase #3 $97.29   5.757%   $102.891   $102.89   $102.90   $102.90  
  Purchase #4 $208.40   3.733%   $216.1796   $216.18   $216.20   $216.20  
  Purchase #5 $76.99   7.492%   $82.7581   $82.76   $82.75   $82.80  
  Purchase #6 $161.91   12.254%   $181.7505   $181.75   $181.75   $181.80  
  Purchase #7 $107.85   13.146%   $122.028   $122.03   $122.05   $122.00  
  7 purchase totals = $954.79       $1,024.2786   $1,024.28   $1,024.30   $1,024.40