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	$147.59	12.195%	$165.5886	$165.59	$165.60	$165.60
Purchase #2	$128.41	12.390%	$144.32	$144.32	$144.30	$144.30
Purchase #3	$248.98	11.474%	$277.548	$277.55	$277.55	$277.50
Purchase #4	$7.73	6.725%	$8.2498	$8.25	$8.25	$8.20
Purchase #5	$50.64	10.193%	$55.8017	$55.80	$55.80	$55.80
Purchase #6	$108.63	9.160%	$118.5805	$118.58	$118.60	$118.60
Purchase #7	$162.82	3.688%	$168.8248	$168.82	$168.80	$168.80
7 purchase totals =	$854.80		$938.9134	$938.91	$938.90	$938.80