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	$81.60	11.119%	$90.6731	$90.67	$90.65	$90.70
Purchase #2	$23.60	11.497%	$26.3133	$26.31	$26.30	$26.30
Purchase #3	$239.46	11.535%	$267.0817	$267.08	$267.10	$267.10
Purchase #4	$27.52	4.274%	$28.6962	$28.70	$28.70	$28.70
Purchase #5	$82.33	8.275%	$89.1428	$89.14	$89.15	$89.10
Purchase #6	$6.66	3.524%	$6.8947	$6.89	$6.90	$6.90
Purchase #7	$123.78	3.623%	$128.2645	$128.26	$128.25	$128.30
7 purchase totals =	$584.95		$637.0663	$637.05	$637.05	$637.10