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	$250.38	10.747%	$277.2883	$277.29	$277.30	$277.30
Purchase #2	$178.49	4.543%	$186.5988	$186.60	$186.60	$186.60
Purchase #3	$175.47	12.147%	$196.7843	$196.78	$196.80	$196.80
Purchase #4	$55.91	6.575%	$59.5861	$59.59	$59.60	$59.60
Purchase #5	$82.99	8.506%	$90.0491	$90.05	$90.05	$90.00
Purchase #6	$114.59	12.130%	$128.4898	$128.49	$128.50	$128.50
Purchase #7	$28.66	13.140%	$32.4259	$32.43	$32.45	$32.40
7 purchase totals =	$886.49		$971.2223	$971.23	$971.30	$971.20