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 $186.42   10.687%   $206.3427   $206.34   $206.35   $206.30  
  Purchase #2 $127.71   11.562%   $142.4758   $142.48   $142.50   $142.50  
  Purchase #3 $245.65   8.259%   $265.9382   $265.94   $265.95   $265.90  
  Purchase #4 $213.26   8.772%   $231.9672   $231.97   $231.95   $232.00  
  Purchase #5 $48.52   12.859%   $54.7592   $54.76   $54.75   $54.80  
  Purchase #6 $154.71   5.591%   $163.3598   $163.36   $163.35   $163.40  
  Purchase #7 $208.71   7.231%   $223.8018   $223.80   $223.80   $223.80  
  7 purchase totals = $1,184.98       $1,288.6447   $1,288.65   $1,288.65   $1,288.70