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	$12.91	5.846%	$13.6647	$13.66	$13.65	$13.70
Purchase #2	$218.42	4.606%	$228.4804	$228.48	$228.50	$228.50
Purchase #3	$105.40	13.775%	$119.9189	$119.92	$119.90	$119.90
Purchase #4	$105.58	4.114%	$109.9236	$109.92	$109.90	$109.90
Purchase #5	$233.89	11.347%	$260.4295	$260.43	$260.45	$260.40
Purchase #6	$183.79	9.238%	$200.7685	$200.77	$200.75	$200.80
Purchase #7	$200.36	11.497%	$223.3954	$223.40	$223.40	$223.40
7 purchase totals =	$1,060.35		$1,156.5810	$1,156.58	$1,156.55	$1,156.60