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	$96.57	4.526%	$100.9408	$100.94	$100.95	$100.90
Purchase #2	$156.74	7.127%	$167.9109	$167.91	$167.90	$167.90
Purchase #3	$220.28	6.711%	$235.063	$235.06	$235.05	$235.10
Purchase #4	$59.92	9.296%	$65.4902	$65.49	$65.50	$65.50
Purchase #5	$90.41	6.743%	$96.5063	$96.51	$96.50	$96.50
Purchase #6	$36.63	6.377%	$38.9659	$38.97	$38.95	$39.00
Purchase #7	$161.27	9.592%	$176.739	$176.74	$176.75	$176.70
7 purchase totals =	$821.82		$881.6161	$881.62	$881.60	$881.60