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	$37.49	12.807%	$42.2913	$42.29	$42.30	$42.30
Purchase #2	$161.86	3.161%	$166.9764	$166.98	$167.00	$167.00
Purchase #3	$30.71	5.526%	$32.407	$32.41	$32.40	$32.40
Purchase #4	$198.71	10.276%	$219.1294	$219.13	$219.15	$219.10
Purchase #5	$95.76	4.477%	$100.0472	$100.05	$100.05	$100.00
Purchase #6	$95.89	4.862%	$100.5522	$100.55	$100.55	$100.60
Purchase #7	$138.94	4.172%	$144.7366	$144.74	$144.75	$144.70
7 purchase totals =	$759.36		$806.1401	$806.15	$806.20	$806.10