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	$222.89	12.818%	$251.46	$251.46	$251.45	$251.50
Purchase #2	$129.41	13.487%	$146.8635	$146.86	$146.85	$146.90
Purchase #3	$95.84	11.215%	$106.5885	$106.59	$106.60	$106.60
Purchase #4	$187.35	10.213%	$206.4841	$206.48	$206.50	$206.50
Purchase #5	$136.55	3.550%	$141.3975	$141.40	$141.40	$141.40
Purchase #6	$134.63	4.807%	$141.1017	$141.10	$141.10	$141.10
Purchase #7	$209.76	9.559%	$229.811	$229.81	$229.80	$229.80
7 purchase totals =	$1,116.43		$1,223.7063	$1,223.70	$1,223.70	$1,223.80