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	$6.83	7.192%	$7.3212	$7.32	$7.30	$7.30
Purchase #2	$31.44	12.503%	$35.3709	$35.37	$35.35	$35.40
Purchase #3	$55.87	5.333%	$58.8495	$58.85	$58.85	$58.80
Purchase #4	$100.72	13.391%	$114.2074	$114.21	$114.20	$114.20
Purchase #5	$162.51	3.799%	$168.6838	$168.68	$168.70	$168.70
Purchase #6	$77.27	10.240%	$85.1824	$85.18	$85.20	$85.20
Purchase #7	$241.50	9.511%	$264.4691	$264.47	$264.45	$264.50
7 purchase totals =	$676.14		$734.0843	$734.08	$734.05	$734.10