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	$171.63	5.651%	$181.3288	$181.33	$181.35	$181.30
Purchase #2	$228.45	12.619%	$257.2781	$257.28	$257.30	$257.30
Purchase #3	$37.95	6.819%	$40.5378	$40.54	$40.55	$40.50
Purchase #4	$18.30	8.774%	$19.9056	$19.91	$19.90	$19.90
Purchase #5	$123.98	4.628%	$129.7178	$129.72	$129.70	$129.70
Purchase #6	$157.64	6.377%	$167.6927	$167.69	$167.70	$167.70
Purchase #7	$72.85	7.817%	$78.5447	$78.54	$78.55	$78.50
7 purchase totals =	$810.80		$875.0055	$875.01	$875.05	$874.90