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	$84.92	13.741%	$96.5889	$96.59	$96.60	$96.60
Purchase #2	$138.97	8.353%	$150.5782	$150.58	$150.60	$150.60
Purchase #3	$53.43	11.869%	$59.7716	$59.77	$59.75	$59.80
Purchase #4	$63.94	12.116%	$71.687	$71.69	$71.70	$71.70
Purchase #5	$128.49	12.190%	$144.1529	$144.15	$144.15	$144.20
Purchase #6	$12.48	4.436%	$13.0336	$13.03	$13.05	$13.00
Purchase #7	$244.47	8.112%	$264.3014	$264.30	$264.30	$264.30
7 purchase totals =	$726.70		$800.1136	$800.11	$800.15	$800.20