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	$37.51	5.328%	$39.5085	$39.51	$39.50	$39.50
Purchase #2	$139.71	3.298%	$144.3176	$144.32	$144.30	$144.30
Purchase #3	$191.88	12.600%	$216.0569	$216.06	$216.05	$216.10
Purchase #4	$39.73	3.425%	$41.0908	$41.09	$41.10	$41.10
Purchase #5	$91.80	4.151%	$95.6106	$95.61	$95.60	$95.60
Purchase #6	$242.36	9.309%	$264.9213	$264.92	$264.90	$264.90
Purchase #7	$231.52	12.191%	$259.7446	$259.74	$259.75	$259.70
7 purchase totals =	$974.51		$1,061.2503	$1,061.25	$1,061.20	$1,061.20