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	$138.93	13.809%	$158.1148	$158.11	$158.10	$158.10
Purchase #2	$74.57	4.781%	$78.1352	$78.14	$78.15	$78.10
Purchase #3	$142.82	8.507%	$154.9697	$154.97	$154.95	$155.00
Purchase #4	$59.64	12.744%	$67.2405	$67.24	$67.25	$67.20
Purchase #5	$237.83	13.135%	$269.069	$269.07	$269.05	$269.10
Purchase #6	$217.53	9.520%	$238.2389	$238.24	$238.25	$238.20
Purchase #7	$226.91	7.331%	$243.5448	$243.54	$243.55	$243.50
7 purchase totals =	$1,098.23		$1,209.3129	$1,209.31	$1,209.30	$1,209.20