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	$89.86	13.670%	$102.1439	$102.14	$102.15	$102.10
Purchase #2	$203.73	3.218%	$210.286	$210.29	$210.30	$210.30
Purchase #3	$78.39	5.207%	$82.4718	$82.47	$82.45	$82.50
Purchase #4	$47.46	4.425%	$49.5601	$49.56	$49.55	$49.60
Purchase #5	$71.79	10.774%	$79.5247	$79.52	$79.50	$79.50
Purchase #6	$29.40	10.129%	$32.3779	$32.38	$32.40	$32.40
Purchase #7	$93.29	8.143%	$100.8866	$100.89	$100.90	$100.90
7 purchase totals =	$613.92		$657.2510	$657.25	$657.25	$657.30