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	$146.48	5.753%	$154.907	$154.91	$154.90	$154.90
Purchase #2	$91.47	10.178%	$100.7798	$100.78	$100.80	$100.80
Purchase #3	$25.86	13.279%	$29.2939	$29.29	$29.30	$29.30
Purchase #4	$119.40	3.803%	$123.9408	$123.94	$123.95	$123.90
Purchase #5	$234.37	7.183%	$251.2048	$251.20	$251.20	$251.20
Purchase #6	$187.31	10.451%	$206.8858	$206.89	$206.90	$206.90
Purchase #7	$108.41	3.228%	$111.9095	$111.91	$111.90	$111.90
7 purchase totals =	$913.30		$978.9216	$978.92	$978.95	$978.90