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	$222.49	13.837%	$253.2759	$253.28	$253.30	$253.30
Purchase #2	$55.78	12.453%	$62.7263	$62.73	$62.75	$62.70
Purchase #3	$103.74	13.760%	$118.0146	$118.01	$118.00	$118.00
Purchase #4	$110.57	4.749%	$115.821	$115.82	$115.80	$115.80
Purchase #5	$19.53	12.219%	$21.9164	$21.92	$21.90	$21.90
Purchase #6	$93.38	13.375%	$105.8696	$105.87	$105.85	$105.90
Purchase #7	$112.61	5.112%	$118.3666	$118.37	$118.35	$118.40
7 purchase totals =	$718.10		$795.9904	$796.00	$795.95	$796.00