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	$172.90	4.631%	$180.907	$180.91	$180.90	$180.90
Purchase #2	$52.37	13.236%	$59.3017	$59.30	$59.30	$59.30
Purchase #3	$198.75	4.597%	$207.8865	$207.89	$207.90	$207.90
Purchase #4	$152.25	13.556%	$172.889	$172.89	$172.90	$172.90
Purchase #5	$177.67	11.805%	$198.6439	$198.64	$198.65	$198.60
Purchase #6	$16.37	13.273%	$18.5428	$18.54	$18.55	$18.50
Purchase #7	$41.48	8.818%	$45.1377	$45.14	$45.15	$45.10
7 purchase totals =	$811.79		$883.3086	$883.31	$883.35	$883.20