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	$65.50	7.287%	$70.273	$70.27	$70.25	$70.30
Purchase #2	$68.43	12.618%	$77.0645	$77.06	$77.05	$77.10
Purchase #3	$219.69	13.761%	$249.9215	$249.92	$249.90	$249.90
Purchase #4	$112.71	9.445%	$123.3555	$123.36	$123.35	$123.40
Purchase #5	$89.32	10.813%	$98.9782	$98.98	$99.00	$99.00
Purchase #6	$220.66	9.774%	$242.2273	$242.23	$242.25	$242.20
Purchase #7	$95.25	7.437%	$102.3337	$102.33	$102.35	$102.30
7 purchase totals =	$871.56		$964.1537	$964.15	$964.15	$964.20