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	$96.72	5.610%	$102.146	$102.15	$102.15	$102.10
Purchase #2	$31.52	7.672%	$33.9382	$33.94	$33.95	$33.90
Purchase #3	$235.77	8.684%	$256.2443	$256.24	$256.25	$256.20
Purchase #4	$7.31	13.185%	$8.2738	$8.27	$8.25	$8.30
Purchase #5	$61.72	5.114%	$64.8764	$64.88	$64.90	$64.90
Purchase #6	$97.66	4.765%	$102.3135	$102.31	$102.30	$102.30
Purchase #7	$106.81	6.601%	$113.8605	$113.86	$113.85	$113.90
7 purchase totals =	$637.51		$681.6527	$681.65	$681.65	$681.60