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	$150.41	6.587%	$160.3175	$160.32	$160.30	$160.30
Purchase #2	$142.96	13.615%	$162.424	$162.42	$162.40	$162.40
Purchase #3	$234.99	3.801%	$243.922	$243.92	$243.90	$243.90
Purchase #4	$163.64	6.634%	$174.4959	$174.50	$174.50	$174.50
Purchase #5	$57.79	5.662%	$61.0621	$61.06	$61.05	$61.10
Purchase #6	$234.34	4.228%	$244.2479	$244.25	$244.25	$244.20
Purchase #7	$212.52	9.758%	$233.2577	$233.26	$233.25	$233.30
7 purchase totals =	$1,196.65		$1,279.7271	$1,279.73	$1,279.65	$1,279.70