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	$48.79	11.543%	$54.4218	$54.42	$54.40	$54.40
Purchase #2	$151.35	9.358%	$165.5133	$165.51	$165.50	$165.50
Purchase #3	$26.34	5.614%	$27.8187	$27.82	$27.80	$27.80
Purchase #4	$15.42	13.466%	$17.4965	$17.50	$17.50	$17.50
Purchase #5	$150.27	9.753%	$164.9258	$164.93	$164.95	$164.90
Purchase #6	$85.79	6.437%	$91.3123	$91.31	$91.30	$91.30
Purchase #7	$59.93	12.315%	$67.3104	$67.31	$67.30	$67.30
7 purchase totals =	$537.89		$588.7988	$588.80	$588.75	$588.70