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	$13.40	13.590%	$15.2211	$15.22	$15.20	$15.20
Purchase #2	$130.51	8.135%	$141.127	$141.13	$141.15	$141.10
Purchase #3	$99.31	10.354%	$109.5926	$109.59	$109.60	$109.60
Purchase #4	$31.51	10.309%	$34.7584	$34.76	$34.75	$34.80
Purchase #5	$168.91	13.569%	$191.8294	$191.83	$191.85	$191.80
Purchase #6	$170.97	6.606%	$182.2643	$182.26	$182.25	$182.30
Purchase #7	$221.49	10.858%	$245.5394	$245.54	$245.55	$245.50
7 purchase totals =	$836.10		$920.3322	$920.33	$920.35	$920.30