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	$134.54	5.499%	$141.9384	$141.94	$141.95	$141.90
Purchase #2	$82.56	8.549%	$89.6181	$89.62	$89.60	$89.60
Purchase #3	$234.87	10.217%	$258.8667	$258.87	$258.85	$258.90
Purchase #4	$118.58	10.281%	$130.7712	$130.77	$130.75	$130.80
Purchase #5	$5.97	6.858%	$6.3794	$6.38	$6.40	$6.40
Purchase #6	$112.91	4.454%	$117.939	$117.94	$117.95	$117.90
Purchase #7	$34.73	3.222%	$35.849	$35.85	$35.85	$35.80
7 purchase totals =	$724.16		$781.3618	$781.37	$781.35	$781.30