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	$89.76	8.862%	$97.7145	$97.71	$97.70	$97.70
Purchase #2	$244.88	13.639%	$278.2792	$278.28	$278.30	$278.30
Purchase #3	$162.60	4.144%	$169.3381	$169.34	$169.35	$169.30
Purchase #4	$117.93	13.562%	$133.9237	$133.92	$133.90	$133.90
Purchase #5	$220.27	9.143%	$240.4093	$240.41	$240.40	$240.40
Purchase #6	$170.54	3.145%	$175.9035	$175.90	$175.90	$175.90
Purchase #7	$225.82	5.218%	$237.6033	$237.60	$237.60	$237.60
7 purchase totals =	$1,231.80		$1,333.1716	$1,333.16	$1,333.15	$1,333.10