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	$102.38	12.152%	$114.8212	$114.82	$114.80	$114.80
Purchase #2	$115.63	10.654%	$127.9492	$127.95	$127.95	$127.90
Purchase #3	$216.34	12.806%	$244.0445	$244.04	$244.05	$244.00
Purchase #4	$105.25	8.296%	$113.9815	$113.98	$114.00	$114.00
Purchase #5	$196.36	9.615%	$215.24	$215.24	$215.25	$215.20
Purchase #6	$52.56	3.510%	$54.4049	$54.40	$54.40	$54.40
Purchase #7	$53.84	9.620%	$59.0194	$59.02	$59.00	$59.00
7 purchase totals =	$842.36		$929.4607	$929.45	$929.45	$929.30