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	$121.56	6.254%	$129.1624	$129.16	$129.15	$129.20
Purchase #2	$146.68	9.393%	$160.4577	$160.46	$160.45	$160.50
Purchase #3	$75.42	13.513%	$85.6115	$85.61	$85.60	$85.60
Purchase #4	$41.53	4.291%	$43.3121	$43.31	$43.30	$43.30
Purchase #5	$63.78	5.710%	$67.4218	$67.42	$67.40	$67.40
Purchase #6	$232.64	7.513%	$250.1182	$250.12	$250.10	$250.10
Purchase #7	$31.33	13.191%	$35.4627	$35.46	$35.45	$35.50
7 purchase totals =	$712.94		$771.5464	$771.54	$771.45	$771.60