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	$250.41	6.402%	$266.4412	$266.44	$266.45	$266.40
Purchase #2	$84.66	7.356%	$90.8876	$90.89	$90.90	$90.90
Purchase #3	$157.59	13.349%	$178.6267	$178.63	$178.65	$178.60
Purchase #4	$64.57	10.757%	$71.5158	$71.52	$71.50	$71.50
Purchase #5	$169.63	13.467%	$192.4741	$192.47	$192.45	$192.50
Purchase #6	$212.30	5.109%	$223.1464	$223.15	$223.15	$223.10
Purchase #7	$26.44	12.554%	$29.7593	$29.76	$29.75	$29.80
7 purchase totals =	$965.60		$1,052.8511	$1,052.86	$1,052.85	$1,052.80