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	$88.91	6.552%	$94.7354	$94.74	$94.75	$94.70
Purchase #2	$70.36	11.251%	$78.2762	$78.28	$78.30	$78.30
Purchase #3	$153.83	9.519%	$168.4731	$168.47	$168.45	$168.50
Purchase #4	$30.51	4.620%	$31.9196	$31.92	$31.90	$31.90
Purchase #5	$21.33	7.477%	$22.9248	$22.92	$22.90	$22.90
Purchase #6	$127.80	13.428%	$144.961	$144.96	$144.95	$145.00
Purchase #7	$113.79	7.163%	$121.9408	$121.94	$121.95	$121.90
7 purchase totals =	$606.53		$663.2309	$663.23	$663.20	$663.20