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	$97.47	8.287%	$105.5473	$105.55	$105.55	$105.50
Purchase #2	$52.82	5.867%	$55.9189	$55.92	$55.90	$55.90
Purchase #3	$201.58	4.378%	$210.4052	$210.41	$210.40	$210.40
Purchase #4	$142.28	3.840%	$147.7436	$147.74	$147.75	$147.70
Purchase #5	$159.74	9.725%	$175.2747	$175.27	$175.25	$175.30
Purchase #6	$56.68	7.869%	$61.1401	$61.14	$61.15	$61.10
Purchase #7	$83.88	6.598%	$89.4144	$89.41	$89.40	$89.40
7 purchase totals =	$794.45		$845.4442	$845.44	$845.40	$845.30