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	$16.84	9.661%	$18.4669	$18.47	$18.45	$18.50
Purchase #2	$228.49	13.655%	$259.6903	$259.69	$259.70	$259.70
Purchase #3	$53.31	11.474%	$59.4268	$59.43	$59.45	$59.40
Purchase #4	$84.81	9.822%	$93.14	$93.14	$93.15	$93.10
Purchase #5	$207.76	12.172%	$233.0485	$233.05	$233.05	$233.00
Purchase #6	$170.55	12.181%	$191.3247	$191.32	$191.30	$191.30
Purchase #7	$6.55	9.126%	$7.1478	$7.15	$7.15	$7.10
7 purchase totals =	$768.31		$862.2450	$862.25	$862.25	$862.10