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	$136.53	12.287%	$153.3054	$153.31	$153.30	$153.30
Purchase #2	$66.31	13.865%	$75.5039	$75.50	$75.50	$75.50
Purchase #3	$110.77	11.612%	$123.6326	$123.63	$123.65	$123.60
Purchase #4	$72.59	8.685%	$78.8944	$78.89	$78.90	$78.90
Purchase #5	$86.98	10.132%	$95.7928	$95.79	$95.80	$95.80
Purchase #6	$153.97	10.625%	$170.3293	$170.33	$170.35	$170.30
Purchase #7	$66.55	13.275%	$75.3845	$75.38	$75.40	$75.40
7 purchase totals =	$693.70		$772.8429	$772.83	$772.90	$772.80