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	$29.73	11.750%	$33.2233	$33.22	$33.20	$33.20
Purchase #2	$52.32	13.621%	$59.4465	$59.45	$59.45	$59.40
Purchase #3	$51.85	3.307%	$53.5647	$53.56	$53.55	$53.60
Purchase #4	$245.58	3.821%	$254.9636	$254.96	$254.95	$255.00
Purchase #5	$86.51	10.440%	$95.5416	$95.54	$95.55	$95.50
Purchase #6	$150.69	13.698%	$171.3315	$171.33	$171.35	$171.30
Purchase #7	$97.79	9.468%	$107.0488	$107.05	$107.05	$107.00
7 purchase totals =	$714.47		$775.1200	$775.11	$775.10	$775.00