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	$187.91	6.873%	$200.8251	$200.83	$200.85	$200.80
Purchase #2	$166.80	13.433%	$189.2062	$189.21	$189.20	$189.20
Purchase #3	$166.79	4.513%	$174.3172	$174.32	$174.30	$174.30
Purchase #4	$60.79	10.387%	$67.1043	$67.10	$67.10	$67.10
Purchase #5	$92.64	8.559%	$100.5691	$100.57	$100.55	$100.60
Purchase #6	$130.49	9.801%	$143.2793	$143.28	$143.30	$143.30
Purchase #7	$42.50	7.319%	$45.6106	$45.61	$45.60	$45.60
7 purchase totals =	$847.92		$920.9118	$920.92	$920.90	$920.90