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	$73.49	10.457%	$81.1748	$81.17	$81.15	$81.20
Purchase #2	$226.93	12.740%	$255.8409	$255.84	$255.85	$255.80
Purchase #3	$21.79	12.766%	$24.5717	$24.57	$24.55	$24.60
Purchase #4	$81.28	12.231%	$91.2214	$91.22	$91.20	$91.20
Purchase #5	$183.54	5.795%	$194.1761	$194.18	$194.20	$194.20
Purchase #6	$50.83	7.437%	$54.6102	$54.61	$54.60	$54.60
Purchase #7	$87.55	3.788%	$90.8664	$90.87	$90.85	$90.90
7 purchase totals =	$725.41		$792.4615	$792.46	$792.40	$792.50