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	$131.84	8.645%	$143.2376	$143.24	$143.25	$143.20
Purchase #2	$97.94	12.429%	$110.113	$110.11	$110.10	$110.10
Purchase #3	$107.31	5.206%	$112.8966	$112.90	$112.90	$112.90
Purchase #4	$120.96	5.695%	$127.8487	$127.85	$127.85	$127.80
Purchase #5	$44.71	12.647%	$50.3645	$50.36	$50.35	$50.40
Purchase #6	$165.38	9.109%	$180.4445	$180.44	$180.45	$180.40
Purchase #7	$6.99	7.410%	$7.508	$7.51	$7.50	$7.50
7 purchase totals =	$675.13		$732.4129	$732.41	$732.40	$732.30