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	$85.71	5.153%	$90.1266	$90.13	$90.15	$90.10
Purchase #2	$5.27	11.842%	$5.8941	$5.89	$5.90	$5.90
Purchase #3	$69.69	9.793%	$76.5147	$76.51	$76.50	$76.50
Purchase #4	$206.79	4.137%	$215.3449	$215.34	$215.35	$215.30
Purchase #5	$18.53	9.775%	$20.3413	$20.34	$20.35	$20.30
Purchase #6	$12.50	6.866%	$13.3583	$13.36	$13.35	$13.40
Purchase #7	$244.69	4.822%	$256.489	$256.49	$256.50	$256.50
7 purchase totals =	$643.18		$678.0689	$678.06	$678.10	$678.00