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	$117.72	3.550%	$121.8991	$121.90	$121.90	$121.90
Purchase #2	$189.29	13.750%	$215.3174	$215.32	$215.30	$215.30
Purchase #3	$218.89	10.819%	$242.5717	$242.57	$242.55	$242.60
Purchase #4	$180.69	5.390%	$190.4292	$190.43	$190.45	$190.40
Purchase #5	$72.71	6.728%	$77.6019	$77.60	$77.60	$77.60
Purchase #6	$41.82	8.611%	$45.4211	$45.42	$45.40	$45.40
Purchase #7	$99.48	8.566%	$108.0015	$108.00	$108.00	$108.00
7 purchase totals =	$920.60		$1,001.2419	$1,001.24	$1,001.20	$1,001.20