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	$29.89	12.468%	$33.6167	$33.62	$33.60	$33.60
Purchase #2	$249.83	12.676%	$281.4985	$281.50	$281.50	$281.50
Purchase #3	$137.95	9.511%	$151.0704	$151.07	$151.05	$151.10
Purchase #4	$78.41	4.658%	$82.0623	$82.06	$82.05	$82.10
Purchase #5	$88.78	12.801%	$100.1447	$100.14	$100.15	$100.10
Purchase #6	$185.97	11.198%	$206.7949	$206.79	$206.80	$206.80
Purchase #7	$242.95	10.444%	$268.3237	$268.32	$268.30	$268.30
7 purchase totals =	$1,013.78		$1,123.5112	$1,123.50	$1,123.45	$1,123.50