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	$166.99	8.179%	$180.6481	$180.65	$180.65	$180.60
Purchase #2	$122.74	3.863%	$127.4814	$127.48	$127.50	$127.50
Purchase #3	$117.87	6.498%	$125.5292	$125.53	$125.55	$125.50
Purchase #4	$53.67	12.530%	$60.3949	$60.39	$60.40	$60.40
Purchase #5	$184.73	8.709%	$200.8181	$200.82	$200.80	$200.80
Purchase #6	$82.34	10.180%	$90.7222	$90.72	$90.70	$90.70
Purchase #7	$97.25	9.735%	$106.7173	$106.72	$106.70	$106.70
7 purchase totals =	$825.59		$892.3112	$892.31	$892.30	$892.20