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	$94.59	9.288%	$103.3755	$103.38	$103.40	$103.40
Purchase #2	$180.93	3.754%	$187.7221	$187.72	$187.70	$187.70
Purchase #3	$69.91	12.270%	$78.488	$78.49	$78.50	$78.50
Purchase #4	$191.46	3.546%	$198.2492	$198.25	$198.25	$198.20
Purchase #5	$139.31	10.278%	$153.6283	$153.63	$153.65	$153.60
Purchase #6	$50.95	13.571%	$57.8644	$57.86	$57.85	$57.90
Purchase #7	$185.55	5.195%	$195.1893	$195.19	$195.20	$195.20
7 purchase totals =	$912.70		$974.5168	$974.52	$974.55	$974.50