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	$156.85	6.586%	$167.1801	$167.18	$167.20	$167.20
Purchase #2	$215.82	11.367%	$240.3523	$240.35	$240.35	$240.40
Purchase #3	$140.59	11.401%	$156.6187	$156.62	$156.60	$156.60
Purchase #4	$221.76	7.599%	$238.6115	$238.61	$238.60	$238.60
Purchase #5	$37.72	11.358%	$42.0042	$42.00	$42.00	$42.00
Purchase #6	$196.36	10.137%	$216.265	$216.27	$216.25	$216.30
Purchase #7	$239.93	5.395%	$252.8742	$252.87	$252.85	$252.90
7 purchase totals =	$1,209.03		$1,313.9060	$1,313.90	$1,313.85	$1,314.00