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	$177.70	4.622%	$185.9133	$185.91	$185.90	$185.90
Purchase #2	$92.94	13.179%	$105.1886	$105.19	$105.20	$105.20
Purchase #3	$137.64	13.207%	$155.8181	$155.82	$155.80	$155.80
Purchase #4	$73.95	11.652%	$82.5667	$82.57	$82.55	$82.60
Purchase #5	$89.42	12.594%	$100.6816	$100.68	$100.70	$100.70
Purchase #6	$71.27	8.196%	$77.1113	$77.11	$77.10	$77.10
Purchase #7	$133.40	10.391%	$147.2616	$147.26	$147.25	$147.30
7 purchase totals =	$776.32		$854.5412	$854.54	$854.50	$854.60