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	$245.76	6.165%	$260.9111	$260.91	$260.90	$260.90
Purchase #2	$172.97	9.350%	$189.1427	$189.14	$189.15	$189.10
Purchase #3	$210.33	13.185%	$238.062	$238.06	$238.05	$238.10
Purchase #4	$152.79	12.559%	$171.9789	$171.98	$172.00	$172.00
Purchase #5	$13.71	13.851%	$15.609	$15.61	$15.60	$15.60
Purchase #6	$79.25	11.446%	$88.321	$88.32	$88.30	$88.30
Purchase #7	$61.66	6.268%	$65.5248	$65.52	$65.50	$65.50
7 purchase totals =	$936.47		$1,029.5495	$1,029.54	$1,029.50	$1,029.50