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	$143.88	8.654%	$156.3314	$156.33	$156.35	$156.30
Purchase #2	$91.61	7.561%	$98.5366	$98.54	$98.55	$98.50
Purchase #3	$38.92	9.546%	$42.6353	$42.64	$42.65	$42.60
Purchase #4	$64.98	4.531%	$67.9242	$67.92	$67.90	$67.90
Purchase #5	$205.56	9.236%	$224.5455	$224.55	$224.55	$224.50
Purchase #6	$102.75	7.621%	$110.5806	$110.58	$110.60	$110.60
Purchase #7	$191.58	4.539%	$200.2758	$200.28	$200.30	$200.30
7 purchase totals =	$839.28		$900.8294	$900.84	$900.90	$900.70