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	$106.59	12.816%	$120.2506	$120.25	$120.25	$120.30
Purchase #2	$59.29	3.857%	$61.5768	$61.58	$61.60	$61.60
Purchase #3	$84.60	8.130%	$91.478	$91.48	$91.50	$91.50
Purchase #4	$198.63	10.466%	$219.4186	$219.42	$219.40	$219.40
Purchase #5	$179.35	3.841%	$186.2388	$186.24	$186.25	$186.20
Purchase #6	$83.56	8.770%	$90.8882	$90.89	$90.90	$90.90
Purchase #7	$21.40	7.778%	$23.0645	$23.06	$23.05	$23.10
7 purchase totals =	$733.42		$792.9155	$792.92	$792.95	$793.00