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	$143.25	9.841%	$157.3472	$157.35	$157.35	$157.30
Purchase #2	$61.94	10.304%	$68.3223	$68.32	$68.30	$68.30
Purchase #3	$172.85	12.344%	$194.1866	$194.19	$194.20	$194.20
Purchase #4	$65.82	10.766%	$72.9062	$72.91	$72.90	$72.90
Purchase #5	$50.85	11.660%	$56.7791	$56.78	$56.80	$56.80
Purchase #6	$30.97	6.112%	$32.8629	$32.86	$32.85	$32.90
Purchase #7	$179.61	6.458%	$191.2092	$191.21	$191.20	$191.20
7 purchase totals =	$705.29		$773.6135	$773.62	$773.60	$773.60