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	$55.28	7.696%	$59.5343	$59.53	$59.55	$59.50
Purchase #2	$170.85	5.757%	$180.6858	$180.69	$180.70	$180.70
Purchase #3	$73.27	4.350%	$76.4572	$76.46	$76.45	$76.50
Purchase #4	$18.50	4.376%	$19.3096	$19.31	$19.30	$19.30
Purchase #5	$191.91	4.181%	$199.9338	$199.93	$199.95	$199.90
Purchase #6	$236.92	13.242%	$268.2929	$268.29	$268.30	$268.30
Purchase #7	$157.88	10.336%	$174.1985	$174.20	$174.20	$174.20
7 purchase totals =	$904.61		$978.4121	$978.41	$978.45	$978.40