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	$127.80	11.418%	$142.3922	$142.39	$142.40	$142.40
Purchase #2	$79.35	3.350%	$82.0082	$82.01	$82.00	$82.00
Purchase #3	$118.97	7.154%	$127.4811	$127.48	$127.50	$127.50
Purchase #4	$175.74	12.635%	$197.9447	$197.94	$197.95	$197.90
Purchase #5	$31.90	12.746%	$35.966	$35.97	$35.95	$36.00
Purchase #6	$94.74	11.718%	$105.8416	$105.84	$105.85	$105.80
Purchase #7	$19.29	4.247%	$20.1092	$20.11	$20.10	$20.10
7 purchase totals =	$647.79		$711.7430	$711.74	$711.75	$711.70