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	$96.31	13.382%	$109.1982	$109.20	$109.20	$109.20
Purchase #2	$155.42	5.783%	$164.4079	$164.41	$164.40	$164.40
Purchase #3	$189.72	5.410%	$199.9839	$199.98	$200.00	$200.00
Purchase #4	$75.57	4.192%	$78.7379	$78.74	$78.75	$78.70
Purchase #5	$151.70	10.341%	$167.3873	$167.39	$167.40	$167.40
Purchase #6	$50.64	7.288%	$54.3306	$54.33	$54.35	$54.30
Purchase #7	$72.99	4.397%	$76.1994	$76.20	$76.20	$76.20
7 purchase totals =	$792.35		$850.2452	$850.25	$850.30	$850.20