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	$49.62	10.728%	$54.9432	$54.94	$54.95	$54.90
Purchase #2	$113.78	5.331%	$119.8456	$119.85	$119.85	$119.80
Purchase #3	$58.99	9.406%	$64.5386	$64.54	$64.55	$64.50
Purchase #4	$67.91	7.668%	$73.1173	$73.12	$73.10	$73.10
Purchase #5	$244.83	9.221%	$267.4058	$267.41	$267.40	$267.40
Purchase #6	$33.49	5.271%	$35.2553	$35.26	$35.25	$35.30
Purchase #7	$54.75	9.269%	$59.8248	$59.82	$59.80	$59.80
7 purchase totals =	$623.37		$674.9306	$674.94	$674.90	$674.80