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	$20.49	6.601%	$21.8425	$21.84	$21.85	$21.80
Purchase #2	$158.42	9.829%	$173.9911	$173.99	$174.00	$174.00
Purchase #3	$90.72	9.652%	$99.4763	$99.48	$99.50	$99.50
Purchase #4	$29.59	7.552%	$31.8246	$31.82	$31.80	$31.80
Purchase #5	$225.93	13.343%	$256.0758	$256.08	$256.10	$256.10
Purchase #6	$82.33	10.631%	$91.0825	$91.08	$91.10	$91.10
Purchase #7	$53.35	12.233%	$59.8763	$59.88	$59.90	$59.90
7 purchase totals =	$660.83		$734.1691	$734.17	$734.25	$734.20