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	$11.97	11.331%	$13.3263	$13.33	$13.35	$13.30
Purchase #2	$127.83	4.467%	$133.5402	$133.54	$133.55	$133.50
Purchase #3	$244.47	13.756%	$278.0993	$278.10	$278.10	$278.10
Purchase #4	$169.46	11.461%	$188.8818	$188.88	$188.90	$188.90
Purchase #5	$249.96	12.194%	$280.4401	$280.44	$280.45	$280.40
Purchase #6	$58.25	7.401%	$62.5611	$62.56	$62.55	$62.60
Purchase #7	$184.82	5.563%	$195.1015	$195.10	$195.10	$195.10
7 purchase totals =	$1,046.76		$1,151.9503	$1,151.95	$1,152.00	$1,151.90