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	$97.30	6.108%	$103.2431	$103.24	$103.25	$103.20
Purchase #2	$47.63	10.418%	$52.5921	$52.59	$52.60	$52.60
Purchase #3	$161.91	7.149%	$173.4849	$173.48	$173.50	$173.50
Purchase #4	$233.31	7.291%	$250.3206	$250.32	$250.30	$250.30
Purchase #5	$189.58	7.786%	$204.3407	$204.34	$204.35	$204.30
Purchase #6	$34.58	8.478%	$37.5117	$37.51	$37.50	$37.50
Purchase #7	$166.80	8.485%	$180.953	$180.95	$180.95	$181.00
7 purchase totals =	$931.11		$1,002.4461	$1,002.43	$1,002.45	$1,002.40