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	$247.71	11.454%	$276.0827	$276.08	$276.10	$276.10
Purchase #2	$209.35	6.868%	$223.7282	$223.73	$223.75	$223.70
Purchase #3	$34.49	5.167%	$36.2721	$36.27	$36.25	$36.30
Purchase #4	$52.53	13.358%	$59.547	$59.55	$59.55	$59.50
Purchase #5	$235.25	13.519%	$267.0534	$267.05	$267.05	$267.10
Purchase #6	$128.30	7.650%	$138.115	$138.12	$138.10	$138.10
Purchase #7	$82.42	10.267%	$90.8821	$90.88	$90.90	$90.90
7 purchase totals =	$990.05		$1,091.6805	$1,091.68	$1,091.70	$1,091.70