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	$245.79	13.485%	$278.9348	$278.93	$278.95	$278.90
Purchase #2	$128.61	9.747%	$141.1456	$141.15	$141.15	$141.10
Purchase #3	$19.73	7.541%	$21.2178	$21.22	$21.20	$21.20
Purchase #4	$39.69	6.535%	$42.2837	$42.28	$42.30	$42.30
Purchase #5	$187.69	9.825%	$206.1305	$206.13	$206.15	$206.10
Purchase #6	$17.82	3.145%	$18.3804	$18.38	$18.40	$18.40
Purchase #7	$144.72	11.154%	$160.8621	$160.86	$160.85	$160.90
7 purchase totals =	$784.05		$868.9549	$868.95	$869.00	$868.90