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	$140.97	7.407%	$151.4116	$151.41	$151.40	$151.40
Purchase #2	$178.91	4.254%	$186.5208	$186.52	$186.50	$186.50
Purchase #3	$150.78	4.819%	$158.0461	$158.05	$158.05	$158.00
Purchase #4	$186.27	13.464%	$211.3494	$211.35	$211.35	$211.30
Purchase #5	$80.70	12.232%	$90.5712	$90.57	$90.55	$90.60
Purchase #6	$63.26	10.681%	$70.0168	$70.02	$70.00	$70.00
Purchase #7	$45.63	11.446%	$50.8528	$50.85	$50.85	$50.90
7 purchase totals =	$846.52		$918.7687	$918.77	$918.70	$918.70