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	$86.78	3.742%	$90.0273	$90.03	$90.05	$90.00
Purchase #2	$158.55	5.700%	$167.5874	$167.59	$167.60	$167.60
Purchase #3	$221.36	8.123%	$239.3411	$239.34	$239.35	$239.30
Purchase #4	$250.52	5.198%	$263.542	$263.54	$263.55	$263.50
Purchase #5	$86.33	5.750%	$91.294	$91.29	$91.30	$91.30
Purchase #6	$181.75	5.327%	$191.4318	$191.43	$191.45	$191.40
Purchase #7	$249.56	13.505%	$283.2631	$283.26	$283.25	$283.30
7 purchase totals =	$1,234.85		$1,326.4867	$1,326.48	$1,326.55	$1,326.40