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	$237.90	12.392%	$267.3806	$267.38	$267.40	$267.40
Purchase #2	$57.78	3.190%	$59.6232	$59.62	$59.60	$59.60
Purchase #3	$170.56	13.292%	$193.2308	$193.23	$193.25	$193.20
Purchase #4	$196.59	6.153%	$208.6862	$208.69	$208.70	$208.70
Purchase #5	$219.65	12.400%	$246.8866	$246.89	$246.90	$246.90
Purchase #6	$88.72	11.764%	$99.157	$99.16	$99.15	$99.20
Purchase #7	$79.78	3.473%	$82.5508	$82.55	$82.55	$82.60
7 purchase totals =	$1,050.98		$1,157.5152	$1,157.52	$1,157.55	$1,157.60