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	$20.84	8.143%	$22.537	$22.54	$22.55	$22.50
Purchase #2	$182.51	9.663%	$200.1459	$200.15	$200.15	$200.10
Purchase #3	$77.30	10.672%	$85.5495	$85.55	$85.55	$85.50
Purchase #4	$80.73	3.321%	$83.411	$83.41	$83.40	$83.40
Purchase #5	$58.96	10.648%	$65.2381	$65.24	$65.25	$65.20
Purchase #6	$75.66	4.747%	$79.2516	$79.25	$79.25	$79.30
Purchase #7	$60.49	11.661%	$67.5437	$67.54	$67.55	$67.50
7 purchase totals =	$556.49		$603.6768	$603.68	$603.70	$603.50