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	$34.74	8.158%	$37.5741	$37.57	$37.55	$37.60
Purchase #2	$104.52	4.589%	$109.3164	$109.32	$109.30	$109.30
Purchase #3	$215.52	7.469%	$231.6172	$231.62	$231.60	$231.60
Purchase #4	$230.47	8.418%	$249.871	$249.87	$249.85	$249.90
Purchase #5	$15.85	10.279%	$17.4792	$17.48	$17.50	$17.50
Purchase #6	$35.33	5.534%	$37.2852	$37.29	$37.30	$37.30
Purchase #7	$86.76	12.849%	$97.9078	$97.91	$97.90	$97.90
7 purchase totals =	$723.19		$781.0509	$781.06	$781.00	$781.10