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	$155.52	8.270%	$168.3815	$168.38	$168.40	$168.40
Purchase #2	$23.99	10.489%	$26.5063	$26.51	$26.50	$26.50
Purchase #3	$78.61	13.281%	$89.0502	$89.05	$89.05	$89.10
Purchase #4	$83.96	11.294%	$93.4424	$93.44	$93.45	$93.40
Purchase #5	$223.27	9.109%	$243.6077	$243.61	$243.60	$243.60
Purchase #6	$20.26	5.359%	$21.3457	$21.35	$21.35	$21.30
Purchase #7	$53.48	4.574%	$55.9262	$55.93	$55.95	$55.90
7 purchase totals =	$639.09		$698.2600	$698.27	$698.30	$698.20