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	$72.87	13.174%	$82.4699	$82.47	$82.45	$82.50
Purchase #2	$245.80	13.250%	$278.3685	$278.37	$278.35	$278.40
Purchase #3	$82.41	4.651%	$86.2429	$86.24	$86.25	$86.20
Purchase #4	$33.65	5.709%	$35.5711	$35.57	$35.55	$35.60
Purchase #5	$165.34	12.301%	$185.6785	$185.68	$185.70	$185.70
Purchase #6	$28.48	6.106%	$30.219	$30.22	$30.20	$30.20
Purchase #7	$54.31	6.411%	$57.7918	$57.79	$57.80	$57.80
7 purchase totals =	$682.86		$756.3417	$756.34	$756.30	$756.40