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	$109.63	12.345%	$123.1638	$123.16	$123.15	$123.20
Purchase #2	$96.95	5.247%	$102.037	$102.04	$102.05	$102.00
Purchase #3	$214.41	4.132%	$223.2694	$223.27	$223.25	$223.30
Purchase #4	$246.40	12.440%	$277.0522	$277.05	$277.05	$277.10
Purchase #5	$171.29	11.533%	$191.0449	$191.04	$191.05	$191.00
Purchase #6	$166.72	13.102%	$188.5637	$188.56	$188.55	$188.60
Purchase #7	$128.42	11.113%	$142.6913	$142.69	$142.70	$142.70
7 purchase totals =	$1,133.82		$1,247.8223	$1,247.81	$1,247.80	$1,247.90