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	$94.84	11.508%	$105.7542	$105.75	$105.75	$105.80
Purchase #2	$91.69	9.315%	$100.2309	$100.23	$100.25	$100.20
Purchase #3	$137.40	8.677%	$149.3222	$149.32	$149.30	$149.30
Purchase #4	$228.62	9.560%	$250.4761	$250.48	$250.50	$250.50
Purchase #5	$72.45	13.750%	$82.4119	$82.41	$82.40	$82.40
Purchase #6	$126.46	7.486%	$135.9268	$135.93	$135.95	$135.90
Purchase #7	$96.43	12.492%	$108.476	$108.48	$108.50	$108.50
7 purchase totals =	$847.89		$932.5981	$932.60	$932.65	$932.60