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	$187.65	12.731%	$211.5397	$211.54	$211.55	$211.50
Purchase #2	$121.56	6.865%	$129.9051	$129.91	$129.90	$129.90
Purchase #3	$128.30	8.833%	$139.6327	$139.63	$139.65	$139.60
Purchase #4	$108.34	4.811%	$113.5522	$113.55	$113.55	$113.60
Purchase #5	$219.46	13.108%	$248.2268	$248.23	$248.25	$248.20
Purchase #6	$49.61	10.208%	$54.6742	$54.67	$54.65	$54.70
Purchase #7	$100.44	10.840%	$111.3277	$111.33	$111.35	$111.30
7 purchase totals =	$915.36		$1,008.8584	$1,008.86	$1,008.90	$1,008.80