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	$116.48	12.797%	$131.3859	$131.39	$131.40	$131.40
Purchase #2	$168.84	10.820%	$187.1085	$187.11	$187.10	$187.10
Purchase #3	$169.63	9.401%	$185.5769	$185.58	$185.60	$185.60
Purchase #4	$121.87	7.819%	$131.399	$131.40	$131.40	$131.40
Purchase #5	$99.58	9.461%	$109.0013	$109.00	$109.00	$109.00
Purchase #6	$24.45	13.512%	$27.7537	$27.75	$27.75	$27.80
Purchase #7	$19.95	9.376%	$21.8205	$21.82	$21.80	$21.80
7 purchase totals =	$720.80		$794.0458	$794.05	$794.05	$794.10