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	$102.57	5.418%	$108.1272	$108.13	$108.15	$108.10
Purchase #2	$52.64	12.601%	$59.2732	$59.27	$59.25	$59.30
Purchase #3	$181.91	9.839%	$199.8081	$199.81	$199.80	$199.80
Purchase #4	$72.73	13.484%	$82.5369	$82.54	$82.55	$82.50
Purchase #5	$78.77	13.530%	$89.4276	$89.43	$89.45	$89.40
Purchase #6	$33.26	8.136%	$35.966	$35.97	$35.95	$36.00
Purchase #7	$247.79	8.406%	$268.6192	$268.62	$268.60	$268.60
7 purchase totals =	$769.67		$843.7582	$843.77	$843.75	$843.70