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	$39.48	5.772%	$41.7588	$41.76	$41.75	$41.80
Purchase #2	$247.33	11.618%	$276.0648	$276.06	$276.05	$276.10
Purchase #3	$220.89	4.535%	$230.9074	$230.91	$230.90	$230.90
Purchase #4	$149.59	12.256%	$167.9238	$167.92	$167.90	$167.90
Purchase #5	$145.75	6.615%	$155.3914	$155.39	$155.40	$155.40
Purchase #6	$57.27	8.214%	$61.9742	$61.97	$61.95	$62.00
Purchase #7	$195.72	7.253%	$209.9156	$209.92	$209.90	$209.90
7 purchase totals =	$1,056.03		$1,143.9360	$1,143.93	$1,143.85	$1,144.00