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	$12.58	4.283%	$13.1188	$13.12	$13.10	$13.10
Purchase #2	$28.29	6.746%	$30.1984	$30.20	$30.20	$30.20
Purchase #3	$76.86	7.623%	$82.719	$82.72	$82.70	$82.70
Purchase #4	$42.27	6.349%	$44.9537	$44.95	$44.95	$45.00
Purchase #5	$59.61	6.478%	$63.4715	$63.47	$63.45	$63.50
Purchase #6	$26.78	6.404%	$28.495	$28.50	$28.50	$28.50
Purchase #7	$74.61	4.560%	$78.0122	$78.01	$78.00	$78.00
7 purchase totals =	$321.00		$340.9686	$340.97	$340.90	$341.00