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	$30.34	3.514%	$31.4061	$31.41	$31.40	$31.40
Purchase #2	$31.56	11.713%	$35.2566	$35.26	$35.25	$35.30
Purchase #3	$224.82	11.503%	$250.681	$250.68	$250.70	$250.70
Purchase #4	$27.86	13.448%	$31.6066	$31.61	$31.60	$31.60
Purchase #5	$54.29	13.870%	$61.82	$61.82	$61.80	$61.80
Purchase #6	$150.75	12.478%	$169.5606	$169.56	$169.55	$169.60
Purchase #7	$122.78	3.688%	$127.3081	$127.31	$127.30	$127.30
7 purchase totals =	$642.40		$707.6390	$707.65	$707.60	$707.70