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	$75.43	4.188%	$78.589	$78.59	$78.60	$78.60
Purchase #2	$190.63	10.383%	$210.4231	$210.42	$210.40	$210.40
Purchase #3	$63.97	11.264%	$71.1756	$71.18	$71.20	$71.20
Purchase #4	$145.62	10.497%	$160.9057	$160.91	$160.90	$160.90
Purchase #5	$68.37	6.203%	$72.611	$72.61	$72.60	$72.60
Purchase #6	$42.65	11.215%	$47.4332	$47.43	$47.45	$47.40
Purchase #7	$114.76	10.290%	$126.5688	$126.57	$126.55	$126.60
7 purchase totals =	$701.43		$767.7064	$767.71	$767.70	$767.70