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	$128.28	6.778%	$136.9748	$136.97	$136.95	$137.00
Purchase #2	$29.29	7.152%	$31.3848	$31.38	$31.40	$31.40
Purchase #3	$207.91	7.592%	$223.6945	$223.69	$223.70	$223.70
Purchase #4	$184.35	6.589%	$196.4968	$196.50	$196.50	$196.50
Purchase #5	$25.46	6.478%	$27.1093	$27.11	$27.10	$27.10
Purchase #6	$12.98	4.469%	$13.5601	$13.56	$13.55	$13.60
Purchase #7	$18.38	13.140%	$20.7951	$20.80	$20.80	$20.80
7 purchase totals =	$606.65		$650.0154	$650.01	$650.00	$650.10