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	$142.90	11.867%	$159.8579	$159.86	$159.85	$159.90
Purchase #2	$36.27	3.271%	$37.4564	$37.46	$37.45	$37.50
Purchase #3	$176.26	11.570%	$196.6533	$196.65	$196.65	$196.70
Purchase #4	$78.78	4.342%	$82.2006	$82.20	$82.20	$82.20
Purchase #5	$98.36	11.631%	$109.8003	$109.80	$109.80	$109.80
Purchase #6	$179.29	6.381%	$190.7305	$190.73	$190.75	$190.70
Purchase #7	$73.29	5.276%	$77.1568	$77.16	$77.15	$77.20
7 purchase totals =	$785.15		$853.8558	$853.86	$853.85	$854.00