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	$46.29	12.488%	$52.0707	$52.07	$52.05	$52.10
Purchase #2	$232.63	3.189%	$240.0486	$240.05	$240.05	$240.00
Purchase #3	$55.30	8.737%	$60.1316	$60.13	$60.15	$60.10
Purchase #4	$73.96	5.532%	$78.0515	$78.05	$78.05	$78.10
Purchase #5	$94.76	13.423%	$107.4796	$107.48	$107.50	$107.50
Purchase #6	$88.32	7.749%	$95.1639	$95.16	$95.15	$95.20
Purchase #7	$167.77	12.581%	$188.8771	$188.88	$188.90	$188.90
7 purchase totals =	$759.03		$821.8230	$821.82	$821.85	$821.90