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	$118.41	10.718%	$131.1012	$131.10	$131.10	$131.10
Purchase #2	$169.63	10.176%	$186.8915	$186.89	$186.90	$186.90
Purchase #3	$235.73	9.670%	$258.5251	$258.53	$258.55	$258.50
Purchase #4	$40.28	11.817%	$45.0399	$45.04	$45.05	$45.00
Purchase #5	$49.53	10.534%	$54.7475	$54.75	$54.75	$54.70
Purchase #6	$26.56	6.627%	$28.3201	$28.32	$28.30	$28.30
Purchase #7	$89.79	9.236%	$98.083	$98.08	$98.10	$98.10
7 purchase totals =	$729.93		$802.7083	$802.71	$802.75	$802.60