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	$99.66	4.297%	$103.9424	$103.94	$103.95	$103.90
Purchase #2	$79.89	4.650%	$83.6049	$83.60	$83.60	$83.60
Purchase #3	$224.29	11.805%	$250.7674	$250.77	$250.75	$250.80
Purchase #4	$24.74	9.543%	$27.1009	$27.10	$27.10	$27.10
Purchase #5	$53.56	12.136%	$60.06	$60.06	$60.05	$60.10
Purchase #6	$98.28	11.862%	$109.938	$109.94	$109.95	$109.90
Purchase #7	$23.86	6.524%	$25.4166	$25.42	$25.40	$25.40
7 purchase totals =	$604.28		$660.8302	$660.83	$660.80	$660.80