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	$80.60	12.641%	$90.7886	$90.79	$90.80	$90.80
Purchase #2	$31.33	12.848%	$35.3553	$35.36	$35.35	$35.40
Purchase #3	$82.63	11.454%	$92.0944	$92.09	$92.10	$92.10
Purchase #4	$146.30	3.608%	$151.5785	$151.58	$151.60	$151.60
Purchase #5	$169.95	7.539%	$182.7625	$182.76	$182.75	$182.80
Purchase #6	$147.31	5.507%	$155.4224	$155.42	$155.40	$155.40
Purchase #7	$47.88	6.806%	$51.1387	$51.14	$51.15	$51.10
7 purchase totals =	$706.00		$759.1404	$759.14	$759.15	$759.20