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	$97.99	12.584%	$110.3211	$110.32	$110.30	$110.30
Purchase #2	$193.50	13.844%	$220.2881	$220.29	$220.30	$220.30
Purchase #3	$212.42	5.226%	$223.5211	$223.52	$223.50	$223.50
Purchase #4	$81.95	5.154%	$86.1737	$86.17	$86.15	$86.20
Purchase #5	$150.42	7.820%	$162.1828	$162.18	$162.20	$162.20
Purchase #6	$18.43	11.167%	$20.4881	$20.49	$20.50	$20.50
Purchase #7	$55.59	11.316%	$61.8806	$61.88	$61.90	$61.90
7 purchase totals =	$810.30		$884.8555	$884.85	$884.85	$884.90