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	$102.31	6.628%	$109.0911	$109.09	$109.10	$109.10
Purchase #2	$205.45	8.456%	$222.8229	$222.82	$222.80	$222.80
Purchase #3	$233.87	10.364%	$258.1083	$258.11	$258.10	$258.10
Purchase #4	$56.96	13.450%	$64.6211	$64.62	$64.60	$64.60
Purchase #5	$32.84	10.846%	$36.4018	$36.40	$36.40	$36.40
Purchase #6	$250.61	7.302%	$268.9095	$268.91	$268.90	$268.90
Purchase #7	$157.41	7.191%	$168.7294	$168.73	$168.75	$168.70
7 purchase totals =	$1,039.45		$1,128.6841	$1,128.68	$1,128.65	$1,128.60