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	$244.58	12.759%	$275.786	$275.79	$275.80	$275.80
Purchase #2	$40.49	8.820%	$44.0612	$44.06	$44.05	$44.10
Purchase #3	$210.50	5.391%	$221.8481	$221.85	$221.85	$221.80
Purchase #4	$174.62	12.486%	$196.4231	$196.42	$196.40	$196.40
Purchase #5	$37.27	3.259%	$38.4846	$38.48	$38.50	$38.50
Purchase #6	$25.80	9.744%	$28.314	$28.31	$28.30	$28.30
Purchase #7	$123.66	11.449%	$137.8178	$137.82	$137.80	$137.80
7 purchase totals =	$856.92		$942.7348	$942.73	$942.70	$942.70