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	$240.32	12.522%	$270.4129	$270.41	$270.40	$270.40
Purchase #2	$80.27	6.756%	$85.693	$85.69	$85.70	$85.70
Purchase #3	$129.45	4.146%	$134.817	$134.82	$134.80	$134.80
Purchase #4	$211.66	5.422%	$223.1362	$223.14	$223.15	$223.10
Purchase #5	$7.36	3.102%	$7.5883	$7.59	$7.60	$7.60
Purchase #6	$220.31	9.207%	$240.5939	$240.59	$240.60	$240.60
Purchase #7	$72.61	9.868%	$79.7752	$79.78	$79.80	$79.80
7 purchase totals =	$961.98		$1,042.0165	$1,042.02	$1,042.05	$1,042.00