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	$231.65	4.592%	$242.2874	$242.29	$242.30	$242.30
Purchase #2	$60.33	10.627%	$66.7413	$66.74	$66.75	$66.70
Purchase #3	$90.93	9.605%	$99.6638	$99.66	$99.65	$99.70
Purchase #4	$96.49	7.587%	$103.8107	$103.81	$103.80	$103.80
Purchase #5	$139.36	8.213%	$150.8056	$150.81	$150.80	$150.80
Purchase #6	$237.41	13.666%	$269.8545	$269.85	$269.85	$269.90
Purchase #7	$236.61	4.317%	$246.8245	$246.82	$246.80	$246.80
7 purchase totals =	$1,092.78		$1,179.9878	$1,179.98	$1,179.95	$1,180.00