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	$171.70	4.714%	$179.7939	$179.79	$179.80	$179.80
Purchase #2	$230.79	8.664%	$250.7856	$250.79	$250.80	$250.80
Purchase #3	$234.64	10.112%	$258.3668	$258.37	$258.35	$258.40
Purchase #4	$248.86	5.800%	$263.2939	$263.29	$263.30	$263.30
Purchase #5	$83.65	6.841%	$89.3725	$89.37	$89.35	$89.40
Purchase #6	$156.56	3.500%	$162.0396	$162.04	$162.05	$162.00
Purchase #7	$65.51	5.777%	$69.2945	$69.29	$69.30	$69.30
7 purchase totals =	$1,191.71		$1,272.9468	$1,272.94	$1,272.95	$1,273.00