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	$166.73	4.523%	$174.2712	$174.27	$174.25	$174.30
Purchase #2	$114.97	8.219%	$124.4194	$124.42	$124.40	$124.40
Purchase #3	$99.52	4.217%	$103.7168	$103.72	$103.70	$103.70
Purchase #4	$41.85	7.655%	$45.0536	$45.05	$45.05	$45.10
Purchase #5	$170.82	3.296%	$176.4502	$176.45	$176.45	$176.50
Purchase #6	$86.72	10.718%	$96.0146	$96.01	$96.00	$96.00
Purchase #7	$99.50	4.528%	$104.0054	$104.01	$104.00	$104.00
7 purchase totals =	$780.11		$823.9312	$823.93	$823.85	$824.00