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	$112.43	7.275%	$120.6093	$120.61	$120.60	$120.60
Purchase #2	$135.56	9.632%	$148.6171	$148.62	$148.60	$148.60
Purchase #3	$132.76	3.479%	$137.3787	$137.38	$137.40	$137.40
Purchase #4	$68.72	5.411%	$72.4384	$72.44	$72.45	$72.40
Purchase #5	$79.48	12.711%	$89.5827	$89.58	$89.60	$89.60
Purchase #6	$79.87	10.243%	$88.0511	$88.05	$88.05	$88.10
Purchase #7	$177.84	7.464%	$191.114	$191.11	$191.10	$191.10
7 purchase totals =	$786.66		$847.7913	$847.79	$847.80	$847.80