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	$127.32	8.322%	$137.9156	$137.92	$137.90	$137.90
Purchase #2	$67.36	5.436%	$71.0217	$71.02	$71.00	$71.00
Purchase #3	$10.30	11.567%	$11.4914	$11.49	$11.50	$11.50
Purchase #4	$206.35	8.302%	$223.4812	$223.48	$223.50	$223.50
Purchase #5	$68.95	4.818%	$72.272	$72.27	$72.25	$72.30
Purchase #6	$141.91	11.413%	$158.1062	$158.11	$158.10	$158.10
Purchase #7	$33.98	12.857%	$38.3488	$38.35	$38.35	$38.30
7 purchase totals =	$656.17		$712.6369	$712.64	$712.60	$712.60