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	$86.31	4.675%	$90.345	$90.35	$90.35	$90.30
Purchase #2	$80.27	12.796%	$90.5413	$90.54	$90.55	$90.50
Purchase #3	$241.39	11.842%	$269.9754	$269.98	$270.00	$270.00
Purchase #4	$179.63	3.336%	$185.6225	$185.62	$185.60	$185.60
Purchase #5	$195.38	4.492%	$204.1565	$204.16	$204.15	$204.20
Purchase #6	$85.29	8.616%	$92.6386	$92.64	$92.65	$92.60
Purchase #7	$154.74	13.112%	$175.0295	$175.03	$175.05	$175.00
7 purchase totals =	$1,023.01		$1,108.3088	$1,108.32	$1,108.35	$1,108.20