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	$100.43	3.700%	$104.1459	$104.15	$104.15	$104.10
Purchase #2	$91.97	9.747%	$100.9343	$100.93	$100.95	$100.90
Purchase #3	$55.36	10.242%	$61.03	$61.03	$61.05	$61.00
Purchase #4	$89.95	10.350%	$99.2598	$99.26	$99.25	$99.30
Purchase #5	$116.93	3.732%	$121.2938	$121.29	$121.30	$121.30
Purchase #6	$160.77	4.744%	$168.3969	$168.40	$168.40	$168.40
Purchase #7	$101.63	3.151%	$104.8324	$104.83	$104.85	$104.80
7 purchase totals =	$717.04		$759.8931	$759.89	$759.95	$759.80