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	$151.76	10.735%	$168.0514	$168.05	$168.05	$168.10
Purchase #2	$152.56	8.223%	$165.105	$165.11	$165.10	$165.10
Purchase #3	$63.42	12.787%	$71.5295	$71.53	$71.55	$71.50
Purchase #4	$75.72	3.721%	$78.5375	$78.54	$78.55	$78.50
Purchase #5	$107.69	11.571%	$120.1508	$120.15	$120.15	$120.20
Purchase #6	$7.78	11.229%	$8.6536	$8.65	$8.65	$8.70
Purchase #7	$58.97	8.342%	$63.8893	$63.89	$63.90	$63.90
7 purchase totals =	$617.90		$675.9171	$675.92	$675.95	$676.00