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	$155.52	5.712%	$164.4033	$164.40	$164.40	$164.40
Purchase #2	$225.59	13.425%	$255.8755	$255.88	$255.90	$255.90
Purchase #3	$64.25	8.281%	$69.5705	$69.57	$69.55	$69.60
Purchase #4	$36.97	6.381%	$39.3291	$39.33	$39.35	$39.30
Purchase #5	$94.38	10.111%	$103.9228	$103.92	$103.90	$103.90
Purchase #6	$156.89	3.440%	$162.287	$162.29	$162.30	$162.30
Purchase #7	$91.79	8.309%	$99.4168	$99.42	$99.40	$99.40
7 purchase totals =	$825.39		$894.8050	$894.81	$894.80	$894.80