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	$37.55	12.212%	$42.1356	$42.14	$42.15	$42.10
Purchase #2	$18.45	3.304%	$19.0596	$19.06	$19.05	$19.10
Purchase #3	$100.79	12.295%	$113.1821	$113.18	$113.20	$113.20
Purchase #4	$212.55	3.658%	$220.3251	$220.33	$220.35	$220.30
Purchase #5	$27.33	5.688%	$28.8845	$28.88	$28.90	$28.90
Purchase #6	$208.63	4.268%	$217.5343	$217.53	$217.55	$217.50
Purchase #7	$98.65	13.266%	$111.7369	$111.74	$111.75	$111.70
7 purchase totals =	$703.95		$752.8581	$752.86	$752.95	$752.80