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 $56.31   11.703%   $62.9   $62.90   $62.90   $62.90  
  Purchase #2 $192.41   7.481%   $206.8042   $206.80   $206.80   $206.80  
  Purchase #3 $180.95   3.130%   $186.6137   $186.61   $186.60   $186.60  
  Purchase #4 $187.59   8.333%   $203.2219   $203.22   $203.20   $203.20  
  Purchase #5 $243.35   10.651%   $269.2692   $269.27   $269.25   $269.30  
  Purchase #6 $191.75   10.124%   $211.1628   $211.16   $211.15   $211.20  
  Purchase #7 $189.64   5.298%   $199.6871   $199.69   $199.70   $199.70  
  7 purchase totals = $1,242.00       $1,339.6589   $1,339.65   $1,339.60   $1,339.70