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	$213.53	8.398%	$231.4622	$231.46	$231.45	$231.50
Purchase #2	$99.94	3.157%	$103.0951	$103.10	$103.10	$103.10
Purchase #3	$42.61	8.357%	$46.1709	$46.17	$46.15	$46.20
Purchase #4	$77.88	4.821%	$81.6346	$81.63	$81.65	$81.60
Purchase #5	$158.82	9.872%	$174.4987	$174.50	$174.50	$174.50
Purchase #6	$127.50	8.281%	$138.0583	$138.06	$138.05	$138.10
Purchase #7	$81.45	9.769%	$89.4069	$89.41	$89.40	$89.40
7 purchase totals =	$801.73		$864.3267	$864.33	$864.30	$864.40