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	$141.77	12.158%	$159.0064	$159.01	$159.00	$159.00
Purchase #2	$84.44	11.673%	$94.2967	$94.30	$94.30	$94.30
Purchase #3	$65.69	7.197%	$70.4177	$70.42	$70.40	$70.40
Purchase #4	$128.59	10.329%	$141.8721	$141.87	$141.85	$141.90
Purchase #5	$144.33	13.869%	$164.3471	$164.35	$164.35	$164.30
Purchase #6	$32.59	8.369%	$35.3175	$35.32	$35.30	$35.30
Purchase #7	$209.78	5.858%	$222.0689	$222.07	$222.05	$222.10
7 purchase totals =	$807.19		$887.3264	$887.34	$887.25	$887.30