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 $247.86   11.658%   $276.7555   $276.76   $276.75   $276.80  
  Purchase #2 $21.96   8.433%   $23.8119   $23.81   $23.80   $23.80  
  Purchase #3 $154.30   7.597%   $166.0222   $166.02   $166.00   $166.00  
  Purchase #4 $142.71   6.304%   $151.7064   $151.71   $151.70   $151.70  
  Purchase #5 $68.40   12.156%   $76.7147   $76.71   $76.70   $76.70  
  Purchase #6 $9.81   11.263%   $10.9149   $10.91   $10.90   $10.90  
  Purchase #7 $226.52   11.310%   $252.1394   $252.14   $252.15   $252.10  
  7 purchase totals = $871.56       $958.0650   $958.06   $958.00   $958.00