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	$72.64	7.812%	$78.3146	$78.31	$78.30	$78.30
Purchase #2	$67.89	10.363%	$74.9254	$74.93	$74.95	$74.90
Purchase #3	$212.60	12.142%	$238.4139	$238.41	$238.40	$238.40
Purchase #4	$154.88	6.403%	$164.797	$164.80	$164.80	$164.80
Purchase #5	$206.60	6.726%	$220.4959	$220.50	$220.50	$220.50
Purchase #6	$140.77	11.134%	$156.4433	$156.44	$156.45	$156.40
Purchase #7	$151.95	12.722%	$171.2811	$171.28	$171.30	$171.30
7 purchase totals =	$1,007.33		$1,104.6712	$1,104.67	$1,104.70	$1,104.60