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	$6.52	12.139%	$7.3115	$7.31	$7.30	$7.30
Purchase #2	$104.97	4.682%	$109.8847	$109.88	$109.90	$109.90
Purchase #3	$99.98	13.109%	$113.0864	$113.09	$113.10	$113.10
Purchase #4	$229.79	11.613%	$256.4755	$256.48	$256.50	$256.50
Purchase #5	$167.95	13.819%	$191.159	$191.16	$191.15	$191.20
Purchase #6	$127.39	7.168%	$136.5213	$136.52	$136.50	$136.50
Purchase #7	$31.49	6.601%	$33.5687	$33.57	$33.55	$33.60
7 purchase totals =	$768.09		$848.0071	$848.01	$848.00	$848.10