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	$34.90	6.620%	$37.2104	$37.21	$37.20	$37.20
Purchase #2	$176.69	10.129%	$194.5869	$194.59	$194.60	$194.60
Purchase #3	$42.54	13.675%	$48.3573	$48.36	$48.35	$48.40
Purchase #4	$82.68	8.641%	$89.8244	$89.82	$89.80	$89.80
Purchase #5	$79.29	11.494%	$88.4036	$88.40	$88.40	$88.40
Purchase #6	$220.32	9.115%	$240.4022	$240.40	$240.40	$240.40
Purchase #7	$141.63	10.535%	$156.5507	$156.55	$156.55	$156.60
7 purchase totals =	$778.05		$855.3355	$855.33	$855.30	$855.40