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	$25.74	6.675%	$27.4581	$27.46	$27.45	$27.50
Purchase #2	$125.30	11.522%	$139.7371	$139.74	$139.75	$139.70
Purchase #3	$67.52	7.258%	$72.4206	$72.42	$72.40	$72.40
Purchase #4	$40.70	9.482%	$44.5592	$44.56	$44.55	$44.60
Purchase #5	$71.86	12.283%	$80.6866	$80.69	$80.70	$80.70
Purchase #6	$200.28	11.653%	$223.6186	$223.62	$223.60	$223.60
Purchase #7	$90.51	11.173%	$100.6227	$100.62	$100.60	$100.60
7 purchase totals =	$621.91		$689.1029	$689.11	$689.05	$689.10