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	$78.58	5.279%	$82.7282	$82.73	$82.75	$82.70
Purchase #2	$148.54	10.735%	$164.4858	$164.49	$164.50	$164.50
Purchase #3	$230.74	8.233%	$249.7368	$249.74	$249.75	$249.70
Purchase #4	$174.67	3.247%	$180.3415	$180.34	$180.35	$180.30
Purchase #5	$100.74	10.198%	$111.0135	$111.01	$111.00	$111.00
Purchase #6	$86.91	9.592%	$95.2464	$95.25	$95.25	$95.20
Purchase #7	$7.32	7.843%	$7.8941	$7.89	$7.90	$7.90
7 purchase totals =	$827.50		$891.4463	$891.45	$891.50	$891.30