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	$59.96	6.768%	$64.0181	$64.02	$64.00	$64.00
Purchase #2	$39.35	10.834%	$43.6132	$43.61	$43.60	$43.60
Purchase #3	$47.58	11.506%	$53.0546	$53.05	$53.05	$53.10
Purchase #4	$211.27	5.483%	$222.8539	$222.85	$222.85	$222.90
Purchase #5	$228.25	9.572%	$250.0981	$250.10	$250.10	$250.10
Purchase #6	$34.40	4.333%	$35.8906	$35.89	$35.90	$35.90
Purchase #7	$176.29	13.301%	$199.7383	$199.74	$199.75	$199.70
7 purchase totals =	$797.10		$869.2668	$869.26	$869.25	$869.30