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	$29.28	6.374%	$31.1463	$31.15	$31.15	$31.10
Purchase #2	$138.88	9.794%	$152.4819	$152.48	$152.50	$152.50
Purchase #3	$86.26	10.281%	$95.1284	$95.13	$95.15	$95.10
Purchase #4	$198.67	12.819%	$224.1375	$224.14	$224.15	$224.10
Purchase #5	$79.53	13.234%	$90.055	$90.06	$90.05	$90.10
Purchase #6	$176.71	4.309%	$184.3244	$184.32	$184.30	$184.30
Purchase #7	$140.41	7.745%	$151.2848	$151.28	$151.30	$151.30
7 purchase totals =	$849.74		$928.5583	$928.56	$928.60	$928.50