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	$121.98	10.504%	$134.7928	$134.79	$134.80	$134.80
Purchase #2	$30.94	9.324%	$33.8248	$33.82	$33.80	$33.80
Purchase #3	$224.38	13.603%	$254.9024	$254.90	$254.90	$254.90
Purchase #4	$130.37	4.423%	$136.1363	$136.14	$136.15	$136.10
Purchase #5	$88.82	13.423%	$100.7423	$100.74	$100.75	$100.70
Purchase #6	$161.74	11.119%	$179.7239	$179.72	$179.70	$179.70
Purchase #7	$10.82	4.141%	$11.2681	$11.27	$11.25	$11.30
7 purchase totals =	$769.05		$851.3906	$851.38	$851.35	$851.30