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	$249.26	9.839%	$273.7847	$273.78	$273.80	$273.80
Purchase #2	$198.47	10.423%	$219.1565	$219.16	$219.15	$219.20
Purchase #3	$169.64	5.690%	$179.2925	$179.29	$179.30	$179.30
Purchase #4	$218.51	12.238%	$245.2513	$245.25	$245.25	$245.30
Purchase #5	$96.61	9.533%	$105.8198	$105.82	$105.80	$105.80
Purchase #6	$18.53	6.577%	$19.7487	$19.75	$19.75	$19.70
Purchase #7	$239.72	7.399%	$257.4569	$257.46	$257.45	$257.50
7 purchase totals =	$1,190.74		$1,300.5104	$1,300.51	$1,300.50	$1,300.60