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	$54.40	5.833%	$57.5732	$57.57	$57.55	$57.60
Purchase #2	$248.55	3.140%	$256.3545	$256.35	$256.35	$256.40
Purchase #3	$37.64	10.202%	$41.48	$41.48	$41.50	$41.50
Purchase #4	$131.44	11.421%	$146.4518	$146.45	$146.45	$146.50
Purchase #5	$203.38	4.847%	$213.2378	$213.24	$213.25	$213.20
Purchase #6	$147.73	7.146%	$158.2868	$158.29	$158.30	$158.30
Purchase #7	$198.63	9.104%	$216.7133	$216.71	$216.70	$216.70
7 purchase totals =	$1,021.77		$1,090.0974	$1,090.09	$1,090.10	$1,090.20