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	$166.39	12.579%	$187.3202	$187.32	$187.30	$187.30
Purchase #2	$57.95	7.464%	$62.2754	$62.28	$62.30	$62.30
Purchase #3	$91.64	13.573%	$104.0783	$104.08	$104.10	$104.10
Purchase #4	$178.85	6.723%	$190.8741	$190.87	$190.85	$190.90
Purchase #5	$153.77	6.753%	$164.1541	$164.15	$164.15	$164.20
Purchase #6	$123.28	6.386%	$131.1527	$131.15	$131.15	$131.20
Purchase #7	$53.61	3.121%	$55.2832	$55.28	$55.30	$55.30
7 purchase totals =	$825.49		$895.1380	$895.13	$895.15	$895.30