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	$88.44	12.874%	$99.8258	$99.83	$99.85	$99.80
Purchase #2	$216.68	11.606%	$241.8279	$241.83	$241.85	$241.80
Purchase #3	$211.96	5.454%	$223.5203	$223.52	$223.50	$223.50
Purchase #4	$238.69	11.602%	$266.3828	$266.38	$266.40	$266.40
Purchase #5	$73.31	8.517%	$79.5538	$79.55	$79.55	$79.60
Purchase #6	$216.37	11.550%	$241.3607	$241.36	$241.35	$241.40
Purchase #7	$208.50	6.709%	$222.4883	$222.49	$222.50	$222.50
7 purchase totals =	$1,253.95		$1,374.9596	$1,374.96	$1,375.00	$1,375.00