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	$114.80	5.306%	$120.8913	$120.89	$120.90	$120.90
Purchase #2	$106.49	4.404%	$111.1798	$111.18	$111.20	$111.20
Purchase #3	$236.43	11.197%	$262.9031	$262.90	$262.90	$262.90
Purchase #4	$86.59	13.470%	$98.2537	$98.25	$98.25	$98.30
Purchase #5	$146.55	9.544%	$160.5367	$160.54	$160.55	$160.50
Purchase #6	$105.32	9.469%	$115.2928	$115.29	$115.30	$115.30
Purchase #7	$29.37	5.796%	$31.0723	$31.07	$31.05	$31.10
7 purchase totals =	$825.55		$900.1297	$900.12	$900.15	$900.20