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	$93.79	6.802%	$100.1696	$100.17	$100.15	$100.20
Purchase #2	$114.98	5.163%	$120.9164	$120.92	$120.90	$120.90
Purchase #3	$36.50	5.632%	$38.5557	$38.56	$38.55	$38.60
Purchase #4	$80.94	10.677%	$89.582	$89.58	$89.60	$89.60
Purchase #5	$207.36	10.776%	$229.7051	$229.71	$229.70	$229.70
Purchase #6	$69.62	10.357%	$76.8305	$76.83	$76.85	$76.80
Purchase #7	$175.37	9.107%	$191.3409	$191.34	$191.35	$191.30
7 purchase totals =	$778.56		$847.1002	$847.11	$847.10	$847.10