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	$198.97	5.726%	$210.363	$210.36	$210.35	$210.40
Purchase #2	$100.41	4.109%	$104.5358	$104.54	$104.55	$104.50
Purchase #3	$212.46	13.166%	$240.4325	$240.43	$240.45	$240.40
Purchase #4	$83.30	8.838%	$90.6621	$90.66	$90.65	$90.70
Purchase #5	$123.68	8.328%	$133.9801	$133.98	$134.00	$134.00
Purchase #6	$54.68	5.570%	$57.7257	$57.73	$57.75	$57.70
Purchase #7	$36.28	11.687%	$40.52	$40.52	$40.50	$40.50
7 purchase totals =	$809.78		$878.2192	$878.22	$878.25	$878.20