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	$115.31	12.708%	$129.9636	$129.96	$129.95	$130.00
Purchase #2	$238.65	6.666%	$254.5584	$254.56	$254.55	$254.60
Purchase #3	$72.36	13.693%	$82.2683	$82.27	$82.25	$82.30
Purchase #4	$248.80	6.291%	$264.452	$264.45	$264.45	$264.50
Purchase #5	$82.62	8.124%	$89.332	$89.33	$89.35	$89.30
Purchase #6	$129.54	7.626%	$139.4187	$139.42	$139.40	$139.40
Purchase #7	$137.68	7.544%	$148.0666	$148.07	$148.05	$148.10
7 purchase totals =	$1,024.96		$1,108.0596	$1,108.06	$1,108.00	$1,108.20