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	$215.67	6.831%	$230.4024	$230.40	$230.40	$230.40
Purchase #2	$104.63	9.803%	$114.8869	$114.89	$114.90	$114.90
Purchase #3	$117.89	6.773%	$125.8747	$125.87	$125.85	$125.90
Purchase #4	$40.50	12.393%	$45.5192	$45.52	$45.50	$45.50
Purchase #5	$33.65	10.412%	$37.1536	$37.15	$37.15	$37.20
Purchase #6	$168.67	12.551%	$189.8398	$189.84	$189.85	$189.80
Purchase #7	$243.34	12.625%	$274.0617	$274.06	$274.05	$274.10
7 purchase totals =	$924.35		$1,017.7383	$1,017.73	$1,017.70	$1,017.80