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	$110.69	12.577%	$124.6115	$124.61	$124.60	$124.60
Purchase #2	$105.72	4.723%	$110.7132	$110.71	$110.70	$110.70
Purchase #3	$133.44	7.590%	$143.5681	$143.57	$143.55	$143.60
Purchase #4	$90.99	13.457%	$103.2345	$103.23	$103.25	$103.20
Purchase #5	$91.77	11.265%	$102.1079	$102.11	$102.10	$102.10
Purchase #6	$93.43	3.253%	$96.4693	$96.47	$96.45	$96.50
Purchase #7	$100.89	11.176%	$112.1655	$112.17	$112.15	$112.20
7 purchase totals =	$726.93		$792.8700	$792.87	$792.80	$792.90