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	$61.34	7.453%	$65.9117	$65.91	$65.90	$65.90
Purchase #2	$81.47	10.393%	$89.9372	$89.94	$89.95	$89.90
Purchase #3	$167.37	4.669%	$175.1845	$175.18	$175.20	$175.20
Purchase #4	$140.64	7.636%	$151.3793	$151.38	$151.40	$151.40
Purchase #5	$96.77	3.374%	$100.035	$100.04	$100.05	$100.00
Purchase #6	$87.84	10.645%	$97.1906	$97.19	$97.20	$97.20
Purchase #7	$74.30	8.104%	$80.3213	$80.32	$80.30	$80.30
7 purchase totals =	$709.73		$759.9596	$759.96	$760.00	$759.90