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	$74.98	6.466%	$79.8282	$79.83	$79.85	$79.80
Purchase #2	$243.83	3.533%	$252.4445	$252.44	$252.45	$252.40
Purchase #3	$202.74	12.222%	$227.5189	$227.52	$227.50	$227.50
Purchase #4	$103.35	10.830%	$114.5428	$114.54	$114.55	$114.50
Purchase #5	$37.39	11.830%	$41.8132	$41.81	$41.80	$41.80
Purchase #6	$157.46	13.529%	$178.7628	$178.76	$178.75	$178.80
Purchase #7	$162.34	5.627%	$171.4749	$171.47	$171.45	$171.50
7 purchase totals =	$982.09		$1,066.3853	$1,066.37	$1,066.35	$1,066.30