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	$25.54	5.654%	$26.984	$26.98	$27.00	$27.00
Purchase #2	$186.86	6.538%	$199.0769	$199.08	$199.10	$199.10
Purchase #3	$147.56	7.164%	$158.1312	$158.13	$158.15	$158.10
Purchase #4	$229.91	12.447%	$258.5269	$258.53	$258.55	$258.50
Purchase #5	$57.75	6.185%	$61.3218	$61.32	$61.30	$61.30
Purchase #6	$171.69	5.512%	$181.1536	$181.15	$181.15	$181.20
Purchase #7	$113.49	4.194%	$118.2498	$118.25	$118.25	$118.20
7 purchase totals =	$932.80		$1,003.4442	$1,003.44	$1,003.50	$1,003.40