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	$128.73	10.566%	$142.3316	$142.33	$142.35	$142.30
Purchase #2	$90.89	10.174%	$100.1371	$100.14	$100.15	$100.10
Purchase #3	$23.74	13.793%	$27.0145	$27.01	$27.00	$27.00
Purchase #4	$45.65	6.429%	$48.5848	$48.58	$48.60	$48.60
Purchase #5	$217.93	5.422%	$229.7462	$229.75	$229.75	$229.70
Purchase #6	$184.28	6.567%	$196.3817	$196.38	$196.40	$196.40
Purchase #7	$62.52	3.391%	$64.6401	$64.64	$64.65	$64.60
7 purchase totals =	$753.74		$808.8360	$808.83	$808.90	$808.70