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	$71.76	6.374%	$76.334	$76.33	$76.35	$76.30
Purchase #2	$147.39	12.149%	$165.2964	$165.30	$165.30	$165.30
Purchase #3	$137.77	11.511%	$153.6287	$153.63	$153.65	$153.60
Purchase #4	$94.27	8.754%	$102.5224	$102.52	$102.50	$102.50
Purchase #5	$89.91	12.687%	$101.3169	$101.32	$101.30	$101.30
Purchase #6	$39.77	5.858%	$42.0997	$42.10	$42.10	$42.10
Purchase #7	$234.61	3.148%	$241.9955	$242.00	$242.00	$242.00
7 purchase totals =	$815.48		$883.1936	$883.20	$883.20	$883.10