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	$39.98	5.817%	$42.3056	$42.31	$42.30	$42.30
Purchase #2	$219.41	11.161%	$243.8984	$243.90	$243.90	$243.90
Purchase #3	$60.67	6.367%	$64.5329	$64.53	$64.55	$64.50
Purchase #4	$151.31	7.566%	$162.7581	$162.76	$162.75	$162.80
Purchase #5	$127.41	8.148%	$137.7914	$137.79	$137.80	$137.80
Purchase #6	$127.27	11.733%	$142.2026	$142.20	$142.20	$142.20
Purchase #7	$136.70	5.737%	$144.5425	$144.54	$144.55	$144.50
7 purchase totals =	$862.75		$938.0315	$938.03	$938.05	$938.00