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	$232.90	9.614%	$255.291	$255.29	$255.30	$255.30
Purchase #2	$37.50	12.404%	$42.1515	$42.15	$42.15	$42.20
Purchase #3	$185.85	6.534%	$197.9934	$197.99	$198.00	$198.00
Purchase #4	$54.48	4.153%	$56.7426	$56.74	$56.75	$56.70
Purchase #5	$102.45	6.307%	$108.9115	$108.91	$108.90	$108.90
Purchase #6	$50.57	7.645%	$54.4361	$54.44	$54.45	$54.40
Purchase #7	$33.88	10.696%	$37.5038	$37.50	$37.50	$37.50
7 purchase totals =	$697.63		$753.0299	$753.02	$753.05	$753.00