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	$150.98	10.674%	$167.0956	$167.10	$167.10	$167.10
Purchase #2	$164.77	8.194%	$178.2713	$178.27	$178.25	$178.30
Purchase #3	$234.50	8.651%	$254.7866	$254.79	$254.80	$254.80
Purchase #4	$33.48	12.241%	$37.5783	$37.58	$37.60	$37.60
Purchase #5	$45.47	9.744%	$49.9006	$49.90	$49.90	$49.90
Purchase #6	$222.27	7.142%	$238.1445	$238.14	$238.15	$238.10
Purchase #7	$49.94	4.520%	$52.1973	$52.20	$52.20	$52.20
7 purchase totals =	$901.41		$977.9742	$977.98	$978.00	$978.00