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	$73.27	11.212%	$81.485	$81.49	$81.50	$81.50
Purchase #2	$91.28	4.570%	$95.4515	$95.45	$95.45	$95.50
Purchase #3	$42.77	8.573%	$46.4367	$46.44	$46.45	$46.40
Purchase #4	$249.37	7.609%	$268.3446	$268.34	$268.35	$268.30
Purchase #5	$137.59	13.351%	$155.9596	$155.96	$155.95	$156.00
Purchase #6	$104.57	8.290%	$113.2389	$113.24	$113.25	$113.20
Purchase #7	$118.51	10.861%	$131.3814	$131.38	$131.40	$131.40
7 purchase totals =	$817.36		$892.2977	$892.30	$892.35	$892.30