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	$42.98	6.122%	$45.6112	$45.61	$45.60	$45.60
Purchase #2	$53.45	4.368%	$55.7847	$55.78	$55.80	$55.80
Purchase #3	$119.97	13.246%	$135.8612	$135.86	$135.85	$135.90
Purchase #4	$247.85	6.786%	$264.6691	$264.67	$264.65	$264.70
Purchase #5	$204.47	6.871%	$218.5191	$218.52	$218.50	$218.50
Purchase #6	$176.59	3.125%	$182.1084	$182.11	$182.10	$182.10
Purchase #7	$172.85	5.184%	$181.8105	$181.81	$181.80	$181.80
7 purchase totals =	$1,018.16		$1,084.3642	$1,084.36	$1,084.30	$1,084.40