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	$232.67	13.156%	$263.2801	$263.28	$263.30	$263.30
Purchase #2	$77.82	4.139%	$81.041	$81.04	$81.05	$81.00
Purchase #3	$71.28	8.641%	$77.4393	$77.44	$77.45	$77.40
Purchase #4	$129.82	13.531%	$147.3859	$147.39	$147.40	$147.40
Purchase #5	$55.50	11.564%	$61.918	$61.92	$61.90	$61.90
Purchase #6	$164.46	12.602%	$185.1852	$185.19	$185.20	$185.20
Purchase #7	$80.57	11.855%	$90.1216	$90.12	$90.10	$90.10
7 purchase totals =	$812.12		$906.3711	$906.38	$906.40	$906.30