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	$70.48	3.548%	$72.9806	$72.98	$73.00	$73.00
Purchase #2	$168.89	12.797%	$190.5029	$190.50	$190.50	$190.50
Purchase #3	$176.28	6.661%	$188.022	$188.02	$188.00	$188.00
Purchase #4	$171.59	7.769%	$184.9208	$184.92	$184.90	$184.90
Purchase #5	$149.80	6.592%	$159.6748	$159.67	$159.65	$159.70
Purchase #6	$137.91	6.266%	$146.5514	$146.55	$146.55	$146.60
Purchase #7	$134.81	8.648%	$146.4684	$146.47	$146.45	$146.50
7 purchase totals =	$1,009.76		$1,089.1209	$1,089.11	$1,089.05	$1,089.20