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	$76.73	4.328%	$80.0509	$80.05	$80.05	$80.10
Purchase #2	$11.40	7.607%	$12.2672	$12.27	$12.25	$12.30
Purchase #3	$123.40	6.812%	$131.806	$131.81	$131.80	$131.80
Purchase #4	$61.38	5.499%	$64.7553	$64.76	$64.75	$64.80
Purchase #5	$73.71	4.581%	$77.0867	$77.09	$77.10	$77.10
Purchase #6	$72.46	9.258%	$79.1683	$79.17	$79.15	$79.20
Purchase #7	$50.40	7.414%	$54.1367	$54.14	$54.15	$54.10
7 purchase totals =	$469.48		$499.2711	$499.29	$499.25	$499.40