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	$190.60	13.274%	$215.9002	$215.90	$215.90	$215.90
Purchase #2	$92.91	8.537%	$100.8417	$100.84	$100.85	$100.80
Purchase #3	$28.96	8.407%	$31.3947	$31.39	$31.40	$31.40
Purchase #4	$125.78	8.404%	$136.3506	$136.35	$136.35	$136.40
Purchase #5	$50.47	3.778%	$52.3768	$52.38	$52.40	$52.40
Purchase #6	$48.44	12.459%	$54.4751	$54.48	$54.50	$54.50
Purchase #7	$187.35	13.519%	$212.6778	$212.68	$212.70	$212.70
7 purchase totals =	$724.51		$804.0169	$804.02	$804.10	$804.10